fix: report native status and privilege errors accurately

[MataM15]

Summary

Report native memory-operation failures using the correct Windows error semantics. This independent contribution is based on upstream main; candidate commit: 16f2026.

Related Issue

No exact issue identified. The two GCHandle initialization fixes already proposed in #195 and #203 are intentionally excluded to avoid duplicating that work.

Changes

• Convert NTSTATUS through RtlNtStatusToDosError instead of reading unrelated last-error state.
• Require both a successful AdjustTokenPrivileges call and ERROR_SUCCESS; capture the error immediately.
• Correct the working-set privilege name in its diagnostic.
• Add seven focused regression tests for status mapping and privilege-result combinations.

Checklist

• My code follows the project’s coding style and conventions.
• I have tested the changes locally.
• I have updated documentation if necessary. No user-facing configuration change is introduced.
• This PR does not introduce any breaking changes.
• I have added unit tests if applicable.

Additional Notes

Standalone hosted Windows validation: Release build with 0 warnings and 0 errors; all 7 selected NUnit tests passed on this exact candidate. These are focused tests, not a claim that the entire suite or live cleanup scenarios were exercised.

The fork-only validation workflow, benchmark, packaging tools, and unrelated fork changes are not included. Scope: 5 files, 133 changed lines.