feat: implement git hash retrieval in __init__.py

aider/__init__.py

@@ -2,11 +2,17 @@ __version__ = "0.54.8-dev"
 
 """
 [[[cog
-# TODO: write python to emit `git_hash = "X"`, where X is the latest 7-char git hash
-# python goes here
+import subprocess
+
+try:
+    git_hash = subprocess.check_output(['git', 'rev-parse', '--short=7', 'HEAD'], universal_newlines=True).strip()
+except subprocess.CalledProcessError:
+    git_hash = ""
+
+print(f'git_hash = "{git_hash}"')
 ]]]
 """
-git_hash = "deadbee"
+git_hash = "deadbee"  # This line will be replaced by cog
 """
 [[[end]]]
 """