Move git utilities into a dedicated crate (#15564)

- create `codex-git-utils` and move the shared git helpers into it with
file moves preserved for diff readability
- move the `GitInfo` helpers out of `core` so stacked rollout work can
depend on the shared crate without carrying its own git info module

---------

Co-authored-by: Ahmed Ibrahim <219906144+aibrahim-oai@users.noreply.github.com>
Co-authored-by: Codex <noreply@openai.com>

codex-rs/cloud-tasks-client/src/http.rs

@@ -16,6 +16,8 @@ use chrono::Utc;
 
 use codex_backend_client as backend;
 use codex_backend_client::CodeTaskDetailsResponseExt;
+use codex_git_utils::ApplyGitRequest;
+use codex_git_utils::apply_git_patch;
 
 #[derive(Clone)]
 pub struct HttpClient {
@@ -459,13 +461,13 @@ mod api {
                 });
             }
 
-            let req = codex_git::ApplyGitRequest {
+            let req = ApplyGitRequest {
                 cwd: std::env::current_dir().unwrap_or_else(|_| std::env::temp_dir()),
                 diff: diff.clone(),
                 revert: false,
                 preflight,
             };
-            let r = codex_git::apply_git_patch(&req)
+            let r = apply_git_patch(&req)
                 .map_err(|e| CloudTaskError::Io(format!("git apply failed to run: {e}")))?;
 
             let status = if r.exit_code == 0 {