feat: baseline lib (#18848)

This add with 2 entry point:
* `reset_git_repository` that takes a directory and set it as a new git
root
* `diff_since_latest_init` this returns the diff for a given directory
since the last `reset_git_repository`

codex-rs/Cargo.toml

@@ -244,6 +244,7 @@ env_logger = "0.11.9"
 eventsource-stream = "0.2.3"
 futures = { version = "0.3", default-features = false }
 gethostname = "1.1.0"
+gix = { version = "0.81.0", default-features = false, features = ["sha1"] }
 glob = "0.3"
 globset = "0.4"
 hmac = "0.12.1"