Investigate cache-hit output and performance for vpr build

Summary

We should investigate the current output and performance characteristics when vpr build hits cache.

Context

From migration/testing follow-up, there are open questions around:

• what output is shown on cache hit
• whether the cache-hit path is performing as expected

Goal

Understand the current behavior on cache hit and identify any follow-up changes needed for UX and/or performance.

Suggested tasks

• Reproduce vpr build cache-hit behavior
• Capture current output shown to users
• Measure/compare cache-hit performance
• Propose or implement follow-up improvements if needed