Add GitHub workflow for sanitizer tests

[naftaly]

• Add new workflow that runs tests with all three sanitizers (thread, address, undefined)
• Sanitizers run in parallel on PRs to catch data races, memory issues, and undefined behavior
• Uses Swift 6.0 matching the benchmarks workflow

[github-actions]

🚀 MemoryMap Performance Benchmarks

256-entry capacity with double hashing, @inline(__always) optimizations

Test Hardware: Apple M1 (Virtual), 7 GB RAM

Core Operations

Operation	Time	Per-Op	Main Thread
Contains	1.0ms	10.0 μs	✅ Excellent
Insert	1.0ms	10.0 μs	✅ Excellent
Lookup (hit)	6.0ms	60.0 μs	✅ Excellent
Lookup (miss)	4.0ms	40.0 μs	✅ Excellent
Mixed operations	5.0ms	25.0 μs	✅ Excellent
Remove (insert+delete)	6.0ms	30.0 μs	✅ Excellent
Update	3.0ms	30.0 μs	✅ Excellent

Load Factor Performance

Load %	Lookups	Time	Per-Lookup	Status
25%	6,400	119ms	18.6 μs	✅ Good
50%	12,800	253ms	19.8 μs	✅ Good
75%	19,200	381ms	19.8 μs	✅ Good
90%	23,000	441ms	19.2 μs	✅ Good
99%	25,300	475ms	18.8 μs	✅ Good

Key Length Impact (100 ops)

Key Length	Time	Per-Op
Long (64 chars)	7.0ms	70.0 μs
Medium (~25 chars)	2.0ms	20.0 μs
Short (2-3 chars)	2.0ms	20.0 μs

Bulk Operations

Operation	Time	Description
Count (100 entries)	4.0ms	✅ Excellent
Keys iteration (100 entries)	0.0ms	✅ Excellent
Large batch write	2.0ms	✅ Excellent
Remove all entries	2.0ms	✅ Excellent
Convert to Dictionary (100 entries)	1.0ms	✅ Excellent

Stress & Edge Cases

Test	Time	Status
Many tombstones	5ms	✅ Good
Random access pattern	6ms	✅ Good
Sequential vs random access	5ms	✅ Good
Worst-case probe chain	74ms	⚠️ OK

Persistence

Operation	Time	Status
Write, close, reopen	3ms	✅ Excellent

Performance Characteristics

Main Thread Budget

• ✅ Excellent: <10ms - Perfect for UI interactions
• ✅ Good: 10-50ms - Acceptable for most operations
• ⚠️ OK: 50-100ms - Use with caution on main thread
• ❌ Review: >100ms - Consider background thread

Target: 16.67ms/frame @ 60fps, 8.33ms/frame @ 120fps

Capacity & Optimization

• Fixed capacity: 256 entries
• Recommended usage: ≤200 keys for optimal performance
• Memory footprint: ~306KB per store
• Key optimizations: Double hashing, @inline(__always), direct buffer access via withUnsafeBytes

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Total tests: 25 passed | Generated 2025-12-27 21:48:48

[Copilot]

Pull request overview

This PR adds a new GitHub Actions workflow to automatically run Swift tests with sanitizers on pull requests. The workflow runs three sanitizers (thread, address, and undefined behavior) in parallel to catch data races, memory issues, and undefined behavior early in the development cycle.

• Adds sanitizer testing infrastructure that runs on all PRs
• Uses Swift 6.0 to match the existing benchmarks workflow
• Implements parallel execution with fail-fast disabled to ensure all sanitizers run

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