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/text/src/anchor.rs

@@ -136,6 +136,7 @@ where
 
 pub trait AnchorRangeExt {
     fn cmp(&self, b: &Range<Anchor>, buffer: &BufferSnapshot) -> Ordering;
+    fn overlaps(&self, b: &Range<Anchor>, buffer: &BufferSnapshot) -> bool;
 }
 
 impl AnchorRangeExt for Range<Anchor> {
@@ -145,4 +146,8 @@ impl AnchorRangeExt for Range<Anchor> {
             ord => ord,
         }
     }
+
+    fn overlaps(&self, other: &Range<Anchor>, buffer: &BufferSnapshot) -> bool {
+        self.start.cmp(&other.end, buffer).is_lt() && other.start.cmp(&self.end, buffer).is_lt()
+    }
 }