perf(ci): reduce queue pressure without paid runners (#23053)

* ci: measure complete unit file costs for shard balancing

* perf(ci): reduce repeated PR setup and capture complete shard timings

* perf(ci): seed reusable main-branch native and typecheck caches

* fix(ci): stop superseded unit workflows from resisting cancellation

* perf(ci): reuse bundle fixtures and share the baseline Git build

* ci: record hosted gains and refresh main hook parity

* ci: retain default workers after performance-budget regression

* docs: record hosted mobile timing flake

---------

Co-authored-by: m4air <m4air@m4airs-Air.localdomain>

.github/workflows/git-command-termination-runtime.yml

@@ -7,6 +7,9 @@ on:
   workflow_dispatch:
 permissions:
   contents: read
+concurrency:
+  group: git-command-termination-${{ github.event.pull_request.number || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 jobs:
   windows-exit:
     runs-on: windows-latest