git: Fix race condition when [un]staging hunks in quick succession (#26422)

- [x] Fix `[un]stage` hunk operations cancelling pending ones
  - [x] Add test
- [ ] bugs I stumbled upon (try to repro again before merging)
  - [x] holding `git::StageAndNext` skips hunks randomly 
    - [x] Add test
  - [x] restoring a file keeps it in the git panel
- [x] Double clicking on `toggle staged` fast makes Zed disagree with
`git` CLI
- [x] checkbox shows ✔️ (fully staged) after a single
stage

Release Notes:

- N/A

---------

Co-authored-by: Cole <cole@zed.dev>
Co-authored-by: Max <max@zed.dev>

crates/buffer_diff/Cargo.toml

@@ -22,6 +22,7 @@ git2.workspace = true
 gpui.workspace = true
 language.workspace = true
 log.workspace = true
+pretty_assertions.workspace = true
 rope.workspace = true
 sum_tree.workspace = true
 text.workspace = true
@@ -31,7 +32,6 @@ util.workspace = true
 ctor.workspace = true
 env_logger.workspace = true
 gpui = { workspace = true, features = ["test-support"] }
-pretty_assertions.workspace = true
 rand.workspace = true
 serde_json.workspace = true
 text = { workspace = true, features = ["test-support"] }