fix(ci,bench): cross-compile abi3, Windows fcntl import, pre-commit cargo

- diffctx/Cargo.toml: enable pyo3 abi3-py310 — arm64 cross-compile no
  longer needs a target python interpreter (was blocking bench-image
  build at maturin --interpreter python3 lookup)
- benchmarks/common.py: defer fcntl import into _bare_repo_lock so
  Windows test matrix can import patch_files without ModuleNotFoundError
- .pre-commit-config.yaml: split cargo test the same way CI does
  (lib in dev, yaml_cases in release) — release+abort+test harness
  conflict surfaces here too
- QA.md: document panic=abort/cargo-test interaction, abi3 cross-compile,
  SonarCloud Bearer auth, recurring rule patterns

Author: nikolay-e

.pre-commit-config.yaml

@@ -274,7 +274,13 @@ repos:
       - id: cargo-test
         name: cargo test (Rust unit tests)
         language: system
-        entry: bash -c 'cd diffctx && DIFFCTX_YAML_CASES_LIMIT=20 cargo test --release'
+        # Two-step: lib unit tests in dev profile (panic=unwind harness),
+        # yaml_cases integration test in release (harness=false, abort-safe).
+        entry: |
+          bash -c '
+          cd diffctx &&
+          cargo test --lib &&
+          DIFFCTX_YAML_CASES_LIMIT=20 cargo test --release --test yaml_cases'
         pass_filenames: false
         files: ^diffctx/.*\.rs$
         types: [file]