Add comprehensive memory leak detection tests

[jgowdy-godaddy]

Summary

Implements comprehensive memory leak detection tests for Asherah's critical components, addressing the final testing recommendation from the remediation guide.

Memory Leak Detection Coverage

Key Areas Tested:

• Key Cache Operations: GetOrLoad, GetOrLoadLatest with same/unique keys
• Reference Counting: Cached crypto key lifecycle management and edge cases
• Session Management: Factory and session creation/cleanup cycles
• Encrypt/Decrypt Operations: Various payload sizes including memory pressure testing
• Concurrent Operations: Session caching behavior under concurrent load
• Goroutine Management: Detection of goroutine leaks in async operations

Test Features

✅ Automatic GC Management: Forces garbage collection for accurate measurements
✅ Configurable Tolerance: 5MB memory growth tolerance with overflow protection
✅ Goroutine Detection: Tracks goroutine leaks with background tolerance
✅ Edge Case Testing: Double close, increment after close, concurrent access
✅ Race Condition Safe: All tests pass with go test -race
✅ Fast Execution: Most tests complete in <1 second
✅ Validation Tests: Intentional leak tests to verify detection works (skipped by default)

Sample Test Results

=== RUN   TestKeyCache_MemoryLeaks/GetOrLoad_SameKey
    memory_leak_test.go:113:   Alloc growth: 0.00 MB
    memory_leak_test.go:114:   TotalAlloc growth: 0.04 MB
    memory_leak_test.go:115:   Sys growth: 0.00 MB
    memory_leak_test.go:116:   GC runs: 2
--- PASS: TestKeyCache_MemoryLeaks/GetOrLoad_SameKey (0.00s)

=== RUN   TestGoroutineLeaks/SessionFactory_Creation_Cleanup
    memory_leak_test.go:410: Goroutine growth: 0 (before: 4, after: 4)
--- PASS: TestGoroutineLeaks/SessionFactory_Creation_Cleanup (0.10s)

Usage

go test -run "MemoryLeaks" -v                 # Run all memory leak tests
go test -race -run "MemoryLeaks" -v          # Run with race detection  
go test -run TestKeyCache_MemoryLeaks -v     # Run specific test category
go test -run TestGoroutineLeaks -v           # Run goroutine leak tests

Implementation Details

• Memory Tracking: Uses runtime.ReadMemStats() with double GC for accuracy
• Leak Detection: Compares before/after stats with configurable tolerance
• Mock Infrastructure: Self-contained test implementations avoid import cycles
• Edge Case Coverage: Tests reference counting failures, double cleanup, etc.
• Production Patterns: Realistic workloads mirror actual usage scenarios

Testing

• ✅ All existing tests pass
• ✅ New memory leak tests execute successfully
• ✅ Race detector verification completed
• ✅ Validation tests confirm leak detection works
• ✅ Edge cases handled without false positives

Test plan

• Run go test -run "MemoryLeaks" -v to verify all memory leak tests
• Run go test -race -run "MemoryLeaks" -v for race condition testing
• Run go test ./... to ensure no regressions
• Verify memory allocation tracking provides meaningful data
• Test both normal operations and edge cases

Completes the final testing recommendation from REMEDIATION.md ✅

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