Add benchmark tests for fileManager module

[pashkov256]

Implement benchmark tests for the FileManager module to measure and improve its performance.

Key areas to benchmark:

• File scanning operations (recursive and non-recursive)
• File filtering operations
• File size calculations
• Concurrent file operations

Technical details:

• Create a new directory: internal/tests/benchmark/filemanager/
• Implement benchmark tests using Go's testing package
• Focus on measuring:
  • Operation time (ns/op)
  • Memory allocations (B/op)
  • Number of allocations (allocs/op)

Example structure:

func BenchmarkFileScanner_ScanFilesRecursively(b *testing.B) {
    // Setup test data
    // Run benchmark
    // Measure performance
}