test: add benchmark tests for performance testing

[devfeel]

Summary

Add benchmark tests for performance testing of FileTarget and JSONTarget.

Benchmark Tests

• • Single thread file write
• • Concurrent file write with multiple goroutines
• • Single thread JSON write
• • Concurrent JSON write
• • Memory usage test
• • File rotation performance

Run Benchmarks

# Run all benchmarks
go test -bench=. -benchtime=3s .

# Run specific benchmark
go test -bench=BenchmarkFileTarget_SingleThreadWrite -benchtime=3s .

Test Results

Benchmark	ops/sec
FileTarget Single	~36,000
FileTarget Concurrent	~80,000
JSONTarget Single	~50,000
FileRotation	~35,000

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