Optimize cache invalidation after directory changes

- Add flush_root_dir_cache() method to selectively clear only __root_dir cache
- Remove redundant flush_caches() before checkout() since checkout flushes anyway
- Use flush_root_dir_cache() instead of flush_caches() when switching to linked worktrees (no checkout follows)

Author: PawelLipski

git_machete/client/traverse.py

@@ -86,8 +86,7 @@ def _switch_to_branch_worktree(
             if current_worktree_root != main_worktree_path:
                 print(f"Changing directory to main worktree at {bold(main_worktree_path)}")
                 os.chdir(main_worktree_path)
-                # Flush cache after directory change so get_root_dir() returns the correct path
-                self._git.flush_caches()
+                # checkout() below will flush all caches, including __root_dir
             self._git.checkout(branch)
             # Update cache after checkout
             self._update_worktrees_cache_after_checkout(branch)
@@ -98,8 +97,8 @@ def _switch_to_branch_worktree(
                 print(f"Branch {bold(branch)} is checked out in worktree at {bold(worktree_path)}")
                 print("Changing directory to that worktree")
                 os.chdir(worktree_path)
-                # Flush cache after directory change so get_root_dir() returns the correct path
-                self._git.flush_caches()
+                # Flush root dir cache after directory change so get_root_dir() returns the correct path
+                self._git.flush_root_dir_cache()
 
     def traverse(
             self,

git_machete/git_operations.py

@@ -256,6 +256,10 @@ def flush_caches(self) -> None:
         self.__root_dir = None
         self.__short_commit_hash_by_revision_cached = {}
 
+    def flush_root_dir_cache(self) -> None:
+        """Flush only the cached root directory. Useful after changing directories with os.chdir()."""
+        self.__root_dir = None
+
     def _run_git(self, git_cmd: str, *args: str, flush_caches: bool, allow_non_zero: bool = False) -> int:
         exit_code = utils.run_cmd(*GIT_EXEC, git_cmd, *args)
         if flush_caches: