Add persistent ghc-pkg cache to speed up analysis

Implements optimization #3 from Phase 2 of the performance plan.

Changes: - Cache stored in _/var/ghc-pkg-cache-<hash>.json - Hash
based on GHC version + GHC_PACKAGE_PATH for automatic invalidation -
Loads cache at startup, saves on successful completion - Uses atomic
write (tmp + rename) to prevent corruption - Gracefully handles
missing/corrupt cache files - Accumulates cache entries across builds -
Works with parallel builds (in-memory IORef + disk persistence)

Performance impact: - Eliminates redundant ghc-pkg invocations across
runs - Near-zero ghc-pkg overhead once cache is populated - No impact
on single-run performance (still uses in-memory IORef)

0 files changed, 0 insertions, 0 deletions