Fix Windows lock ordering and config decode fallback

[wkramme]

Summary

This PR includes the generic core fix set for Windows lock behavior and config decoding hardening:

• acquire the Windows byte lock before normalizing/truncating the lock sidecar
• normalize sidecar size only while the lock is held
• best-effort prime for empty lock sidecars so contention errors do not leak
• decode config using utf-8-sig (BOM-safe) with a narrow Windows locale fallback for legacy files
• preserve strict corruption handling and quarantine behavior

Why

A review flagged a lock-ordering issue: sidecar mutation could happen before lock acquisition and potentially leak OSError under contention. This change ensures ordering is lock-first, mutate-after-acquire.

Tests

Added/updated targeted coverage for:

• Windows lock sidecar normalization behavior
• contention regression: sidecar is not mutated until lock acquisition
• empty-sidecar prime path swallowing transient write error
• UTF-8 BOM config decode acceptance
• Windows locale fallback decode handling and warning path

Validation run

• pytest -q -o addopts='' tests/test_atomic_io.py tests/test_config_corruption_resilience.py → 40 passed
• ruff check code_puppy/atomic_io.py code_puppy/config_file.py tests/test_atomic_io.py tests/test_config_corruption_resilience.py → passed

Notes

• Generic/open-source-safe change; no Walmart-specific behavior.

[wkramme]

Addressed CI formatting failure by running Ruff formatter on tests/test_config_corruption_resilience.py and pushing an update (commit 21edfde).\n\nVerification after update:\n- ruff format --check . \n- ruff check on touched files \n- targeted pytest suite (tests/test_atomic_io.py + tests/test_config_corruption_resilience.py): 40 passed

[thomwebb]

Reviewed the complete generic fix set. The Windows lock ordering issue from the internal draft is resolved: oversized sidecars are normalized only after acquisition, empty-sidecar priming preserves polling behavior, and the added contention regression verifies the sidecar remains untouched until the lock is acquired. The UTF-8/BOM and Windows locale fallback changes are appropriately scoped and covered. All four implementation/test files belong upstream; quality, macOS, and Windows encoding checks are green. Looks good to merge.