chore: Fall back on shared libzstd if libzstd_static is not available (#704)

This PR updates the CMake such that it works in conda after a `conda
install zstd` (which doesn't provide `libzstd_static`, but does provide
`libzstd`). This is needed to unskip the integration tests for zstd
because the integration image uses conda (
apache/arrow#45205 ).

Previous commits tested apache/arrow#45205 by
specifically pulling that branch instead of apache/arrow. When zstd is
installed...the tests pass!

Author: paleolimbot

CMakeLists.txt

@@ -210,7 +210,14 @@ if(NANOARROW_IPC)
   if(NANOARROW_IPC_WITH_ZSTD)
     find_package(zstd REQUIRED)
     set(NANOARROW_IPC_EXTRA_FLAGS "-DNANOARROW_IPC_WITH_ZSTD")
-    set(NANOARROW_IPC_EXTRA_LIBS zstd::libzstd_static)
+
+    # libzstd_static is not available from conda
+    # This could be configurable if shared zstd is a must
+    if(TARGET zstd::libzstd_static)
+      set(NANOARROW_IPC_EXTRA_LIBS zstd::libzstd_static)
+    else()
+      set(NANOARROW_IPC_EXTRA_LIBS zstd::libzstd)
+    endif()
   endif()
 
   if(NOT NANOARROW_BUNDLE)