fix: intermittent stale push statusline after commit

[martinabeleda]

Summary

This fixes an intermittent issue where, after committing, the statusline sometimes failed to update the ↑N commits to push indicator right away.

Root cause (observed behavior)

Immediately after git commit, the first snapshot refresh could occasionally return stale upstream/ahead state, causing the statusline to continue showing the previous
unpushed count.

What changed

• App::refresh refactor
  • Added refresh_now() for immediate refreshes.
  • refresh() still enforces debounce.
  • force_refresh() now uses direct non-debounced refresh.
• Post-commit refresh hardening
  • In execute_commit(), capture previous_unpushed.
  • After successful commit, refresh once.
  • If unpushed count did not advance (after <= before), refresh a second time.
• Testability + regression coverage
  • Extracted logic into refresh_unpushed_after_commit(...).
  • Added tests:
    - refresh_unpushed_after_commit_retries_when_first_refresh_is_stale
    - refresh_unpushed_after_commit_does_not_retry_when_unpushed_advances

Why this is safe

• Retry is narrowly scoped to successful commit flow.
• Second refresh only occurs when the first result looks stale.
• Existing debounce behavior for normal periodic refresh remains unchanged.

Testing

• Added targeted unit tests for retry/no-retry behavior.
• Ran full suite:

  cargo test -q

All tests pass.