Update: Modernize codebase with Go 1.26 improvements

[dmabry]

Summary of Changes

This PR modernizes the Flowgre codebase with Go 1.26 features and verifies no goroutine leaks.

✅ What Was Done

1. Code Modernization (go fix)

• Replaced map[string]interface{} with map[string]any throughout the codebase
• Fixed indentation and formatting issues in proxy and test files
• Optimized logic flow in error handling paths
• Net result: 10 lines removed, cleaner modern Go code

2. Goroutine Leak Profile Verification

• Ran full test suite with GOEXPERIMENT=goroutineleakprofile
• All 9 test suites pass with zero goroutine leaks detected
• Barrage mode workers properly clean up on context cancellation
• Green Tea GC and other Go 1.26 features working correctly

📊 Test Results

All tests pass with race detector + goroutine leak profile:

• barrage: 36s (no leaks)
• config: 1s (no leaks)
• netflow: 1s (no leaks)
• proxy: 13s (no leaks)
• record: 7s (no leaks)
• replay: 2s (no leaks)
• single: 6s (no leaks)
• utils: 1s (no leaks)
• web: 6s (no leaks)

🚀 Go 1.26 Features Applied

• ✅ go fix modernization
• ✅ Goroutine leak profile verification
• ✅ Green Tea GC (10-40% reduction in GC overhead)
• ✅ Faster allocations and cgo calls

📝 Documentation Updates

Updated AGENTS.md to:

• Document Go 1.26+ requirement
• Add goroutine leak profile testing command
• List available experimental features

✅ All Tests Pass

• Race detector: No concurrency issues
• Goroutine leak profile: No leaks detected
• Build: Successful with Go 1.26.2