Minor code clean-up

[jmid]

This little PR changes the 3 remaining property functions to be written using a syntactic function header.
I noticed while merging main into #112.

As an added bonus we avoid a little indentation 😅

[jmid]

Besides usual suspects (2 Dynlink + 3 Threadomain failures) CI triggered a Linux trunk failure on Sys tests:
https://github.com/ocaml-multicore/multicoretests/actions/runs/4075448085/jobs/7021852630

random seed: 236496739
generated error fail pass / total     time test name

[ ]    0    0    0    0 / 1000     0.0s STM Sys test sequential
[ ]    0    0    0    0 / 1000     0.0s STM Sys test sequential (generating)
[✓] 1000    0    0 1000 / 1000     3.3s STM Sys test sequential

[ ]    0    0    0    0 /  200     0.0s STM Sys test parallel
[ ]   64    0    0   64 /  200    56.8s STM Sys test parallel
[ ]  108    0    0  108 /  200   116.9s STM Sys test parallel
[ ]  119    0    0  119 /  200   177.3s STM Sys test parallel (shrinking:    6.0003)
[✗]  120    0    1  119 /  200   235.6s STM Sys test parallel

--- Failure --------------------------------------------------------------------

Test STM Sys test parallel failed (10 shrink steps):

File "src/sys/dune", line 4, characters 7-16:
                                                        |                      
4 |  (name stm_tests)
           ^^^^^^^^^
(cd _build/default/src/sys && ./stm_tests.exe --verbose)
Command exited with code 1.
                                  (Readdir ["ccc"; "ccc"; "ccc"; "bbb"; "ccc"])
                                                        |                      
                                .----------------------------------------------.
                                |                                              |                      
                      (File_exists ["eee"])                        (Mkfile (["aaa"], "aaa"))          
                      (Mkfile ([], "ddd"))                  (Rmdir (["bbb"; "ccc"; "bbb"], "ccc"))    
                        (Readdir ["ddd"])                          (Mkfile (["aaa"], "ddd"))          
                      (File_exists ["ddd"])                              (Readdir [])                 
                      (File_exists ["ddd"])                           (Mkdir ([], "aaa"))             
                    (Mkdir (["bbb"], "ccc"))                           (Readdir ["aaa"])              
                       (Rmdir ([], "aaa"))               (Rmdir (["ccc"; "aaa"; "ddd"; "ddd"], "aaa"))
          (Mkdir (["eee"; "eee"; "ccc"; "eee"], "ddd"))            (Mkdir (["aaa"], "ccc"))           
                       (Rmdir ([], "bbb"))                           (File_exists ["aaa"])            


+++ Messages ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Messages for test STM Sys test parallel:

  Results incompatible with linearized model

                                                                                                                                 |                                                              
                                                                    (Readdir ["ccc"; "ccc"; "ccc"; "bbb"; "ccc"]) : Error (Sys_error("_sandbox/ccc/ccc/ccc/bbb/ccc: No such file or directory"))
                                                                                                                                 |                                                              
                                                                  .-----------------------------------------------------------------------------------------------------------------------------.
                                                                  |                                                                                                                             |                                                              
                                                    (File_exists ["eee"]) : false                                                                  (Mkfile (["aaa"], "aaa")) : Error (Sys_error("_sandbox/aaa/aaa: No such file or directory"))                
                                                    (Mkfile ([], "ddd")) : Ok (())                                                      (Rmdir (["bbb"; "ccc"; "bbb"], "ccc")) : Error (Sys_error("_sandbox/bbb/ccc/bbb/ccc: No such file or directory"))      
                                (Readdir ["ddd"]) : Error (Sys_error("_sandbox/ddd: Not a directory"))                                             (Mkfile (["aaa"], "ddd")) : Error (Sys_error("_sandbox/aaa/ddd: No such file or directory"))                
                                                     (File_exists ["ddd"]) : true                                                                                                 (Readdir []) : Ok ([|"ddd"|])                                                
                                                     (File_exists ["ddd"]) : true                                                                                                 (Mkdir ([], "aaa")) : Ok (())                                                
                     (Mkdir (["bbb"], "ccc")) : Error (Sys_error("_sandbox/bbb/ccc: No such file or directory"))                                                                  (Readdir ["aaa"]) : Ok ([||])                                                
                                                    (Rmdir ([], "aaa")) : Ok (())                                                  (Rmdir (["ccc"; "aaa"; "ddd"; "ddd"], "aaa")) : Error (Sys_error("_sandbox/ccc/aaa/ddd/ddd/aaa: No such file or directory"))
     (Mkdir (["eee"; "eee"; "ccc"; "eee"], "ddd")) : Error (Sys_error("_sandbox/eee/eee/ccc/eee/ddd: No such file or directory"))                  (Mkdir (["aaa"], "ccc")) : Error (Sys_error("_sandbox/aaa/ccc: No such file or directory"))                 
                          (Rmdir ([], "bbb")) : Error (Sys_error("_sandbox/bbb: No such file or directory"))                                                                       (File_exists ["aaa"]) : true                                                

================================================================================
failure (1 tests failed, 0 tests errored, ran 2 tests)

[shym]

Unfortunately, this is an instance of the pattern: rmdir aaa in parallel with mkdir aaa/bbb; file_exists aaa, in which mkdir fails because aaa is already being removed, while file_exists succeeds because the aaa still exists a bit (in my tests for that very case, the stat syscall succeeds but reports that the inode has no physical links left, aka it does not exist...).
See this comment for details.