chore: add devenv option to not install git hooks (#1015)

Tested with and without a `devenv.local.nix` with 
```
{
  hugr.installGitHooks = false;
}
```

devenv.nix

@@ -1,52 +1,61 @@
-{ pkgs, lib, inputs, ... }:
+{ pkgs, lib, inputs, config, ... }:
 let
   pkgs-stable = import inputs.nixpkgs-stable { system = pkgs.stdenv.system; };
+  cfg = config.hugr;
 in
 {
-  # https://devenv.sh/packages/
-  # on macos frameworks have to be explicitly specified
-  # otherwise a linker error ocurs on rust packages
-  packages = [
-    pkgs.just
-    pkgs.llvmPackages_16.libllvm
-    # cargo-llvm-cov is currently marked broken on nixpkgs unstable
-    pkgs-stable.cargo-llvm-cov
-  ] ++ lib.optionals
-    pkgs.stdenv.isDarwin
-    (with pkgs.darwin.apple_sdk; [
-      frameworks.CoreServices
-      frameworks.CoreFoundation
-      # added for json schema validation tests
-      frameworks.SystemConfiguration
-    ]);
+  options.hugr = {
+    setupInShell = lib.mkEnableOption "setupInShell" // {
+      default = true;
+      description = "run `just setup` on entering shell";
+    };
+  };
 
-  # https://devenv.sh/scripts/
-  scripts.hello.exec = "echo Welcome to hugr dev shell!";
+  config = {
+    # https://devenv.sh/packages/
+    # on macos frameworks have to be explicitly specified
+    # otherwise a linker error ocurs on rust packages
+    packages = [
+      pkgs.just
+      pkgs.llvmPackages_16.libllvm
+      # cargo-llvm-cov is currently marked broken on nixpkgs unstable
+      pkgs-stable.cargo-llvm-cov
+    ] ++ lib.optionals
+      pkgs.stdenv.isDarwin
+      (with pkgs.darwin.apple_sdk; [
+        frameworks.CoreServices
+        frameworks.CoreFoundation
+        # added for json schema validation tests
+        frameworks.SystemConfiguration
+      ]);
 
-  enterShell = ''
-    hello
-    cargo --version
-    export LLVM_COV="${pkgs.llvmPackages_16.libllvm}/bin/llvm-cov"
-    export LLVM_PROFDATA="${pkgs.llvmPackages_16.libllvm}/bin/llvm-profdata"
+    # https://devenv.sh/scripts/
+    scripts.hello.exec = "echo Welcome to hugr dev shell!";
 
-    just setup
-  '';
+    enterShell = ''
+      hello
+      cargo --version
+      export LLVM_COV="${pkgs.llvmPackages_16.libllvm}/bin/llvm-cov"
+      export LLVM_PROFDATA="${pkgs.llvmPackages_16.libllvm}/bin/llvm-profdata"
+    '' + lib.optionalString cfg.setupInShell ''
+      just setup
+    '';
 
-  languages.python = {
-    enable = true;
-    poetry = {
+    languages.python = {
       enable = true;
-      activate.enable = true;
+      poetry = {
+        enable = true;
+        activate.enable = true;
+      };
     };
-  };
 
-  # https://devenv.sh/languages/
-  # https://devenv.sh/reference/options/#languagesrustversion
-  languages.rust = {
-    channel = "stable";
-    enable = true;
-    components = [ "rustc" "cargo" "clippy" "rustfmt" "rust-analyzer" ];
+    # https://devenv.sh/languages/
+    # https://devenv.sh/reference/options/#languagesrustversion
+    languages.rust = {
+      channel = "stable";
+      enable = true;
+      components = [ "rustc" "cargo" "clippy" "rustfmt" "rust-analyzer" ];
+    };
   };
-
   # See full reference at https://devenv.sh/reference/options/
 }

justfile

@@ -6,7 +6,8 @@ help:
 # setting up the pre-commit hooks.
 setup:
     poetry install
-    poetry run pre-commit install -t pre-commit
+    # setup git hooks unless environment variable HUGR_JUST_INHIBIT_GIT_HOOKS is non-empty
+    [[ -z $HUGR_JUST_INHIBIT_GIT_HOOKS ]] && poetry run pre-commit install -t pre-commit || true
 
 # Run the pre-commit checks.
 check: