POC Exceptions thrown on errors even when validation succeeds

[westin-m]

Show that returning ValidationResult objects reduces allocations and latency vs. throwing exceptions in multi-policy success cases

• Create/reuse a minimal multi-policy harness that reproduces the current behavior
  • Benchmarks exist in the perf folder and can be used as a reference
• Prototype a result object that captures per-policy failures + final success/failure
• Plumb the result through one end-to-end call path and ensure exceptions are only thrown for final failure (or truly exceptional cases)

acceptance criteria

• Zero intermediate exceptions in success scenario
• Reduced latency and allocations vs. throwing exceptions