Add git metadata handling and integration tests for sync direction defaults

- Introduced new tests for git-based sync direction defaults, verifying the presence of git metadata and correct mappings of changed files to instance references.
- Enhanced the `compute_git_metadata` function to include canonical paths for repository roots.
- Added multiple test cases to ensure accurate behavior of `changedIds` and `scriptCommittedHashes` based on git status.
- Created a new project structure for testing, including various script and model files to facilitate comprehensive testing of git integration.

These changes improve the robustness of the git synchronization features and ensure reliable behavior in various scenarios.

rojo-test/serve-tests/git_sync_defaults/src/ClientScript.client.luau

@@ -0,0 +1 @@
+print("Hello from client")

rojo-test/serve-tests/git_sync_defaults/src/DirModule/Child.luau

@@ -0,0 +1 @@
+return "child"

rojo-test/serve-tests/git_sync_defaults/src/DirModule/init.luau

@@ -0,0 +1,2 @@
+local DirModule = {}
+return DirModule

rojo-test/serve-tests/git_sync_defaults/src/ModuleA.luau

@@ -0,0 +1,2 @@
+local ModuleA = {}
+return ModuleA

rojo-test/serve-tests/git_sync_defaults/src/ServerScript.server.luau

@@ -0,0 +1 @@
+print("Hello from server")

rojo-test/serve-tests/git_sync_defaults/src/SimpleModel.model.json5

@@ -0,0 +1,6 @@
+{
+  "className": "Part",
+  "properties": {
+    "Anchored": true
+  }
+}