Reduce filter, hashing, and cache overhead in core paths

[cofin]

Summary

Filter processing, parameter hashing, and cache operations should avoid avoidable allocations, lock work, and debug formatting on common paths.

Scope

• Tighten filter conflict-resolution and hashing helpers.
• Avoid unnecessary debug-message construction when debug logging is disabled.
• Reduce cache locking overhead while preserving cache correctness.
• Preserve public filter and cache behavior.

Validation

Covered by filter, hashing, cache, and core unit tests in PR #545.