Task E: Enhanced Preprocessor and ImportTracker Integration

Status: ✅ SUCCESS

Summary: Integrated FunctionExclusionCache into preprocessor pipeline with optional cache support, early bailout optimization, and full backward compatibility.

Implementation:
- Added cache field to Preprocessor struct (optional, nil-safe)
- Created internal newWithConfigAndCache() constructor
- Updated NewWithCache() in package_context.go to use cache
- Implemented early bailout in Process() method (GPT-5.1 optimization)
- Added HasUnqualifiedImports() getter to FunctionExclusionCache
- Added GetCache() and HasCache() accessor methods to Preprocessor

Tests: 6/6 passing (100%)
- TestPreprocessor_WithCache: Cache integration ✅
- TestPreprocessor_WithoutCache: Backward compatibility ✅
- TestPreprocessor_EarlyBailout: Optimization (no unqualified) ✅
- TestPreprocessor_EarlyBailout_HasUnqualified: With unqualified calls ✅
- TestPreprocessor_NilCache: Nil-safety ✅
- TestNewWithMainConfig_BackwardCompat: Old API works ✅

Files Modified:
- pkg/preprocessor/preprocessor.go (+40 lines)
- pkg/preprocessor/package_context.go (-3 lines, simplified)
- pkg/preprocessor/function_cache.go (+7 lines, HasUnqualifiedImports method)

Files Created:
- pkg/preprocessor/preprocessor_cache_test.go (+300 lines, 6 tests)

Performance:
- No cache: Zero overhead (nil check only)
- With cache: Early bailout saves processing when no unqualified imports
- Memory: 8 bytes per preprocessor (pointer to shared cache)

Backward Compatibility: ✅ PRESERVED
- All existing constructors work unchanged
- New() → no cache
- NewWithConfig() → no cache
- NewWithMainConfig() → no cache
- NewWithCache() → with cache (new)

Integration Readiness:
✅ Ready for Task D (UnqualifiedImportProcessor)
- Cache accessible via GetCache()
- Early bailout flag ready (skipUnqualifiedProcessing)
- Local function exclusion: cache.IsLocalSymbol(name)
- All infrastructure in place

Next Steps:
1. Task D: Create UnqualifiedImportProcessor
2. Register in processor pipeline (when cache != nil)
3. Use cache.IsLocalSymbol() for exclusion
4. Use skipUnqualifiedProcessing flag for early bailout

Details: See task-E-changes.md and task-E-notes.md
