feat: add comprehensive performance benchmarks issue#21

[Sukuna0007Abhi]

Add comprehensive performance benchmarks

Summary

This PR implements comprehensive performance benchmarks for the CMW library to establish performance baselines and enable data-driven optimization decisions.

Changes

• Added benchmark_test.go with 40+ performance benchmarks covering:

  • JSON/CBOR marshaling and unmarshaling for different data sizes
  • X.509 extension encoding/decoding operations
  • Format detection and auto-deserialization
  • Collection operations and nested data structures
  • CBOR tag format vs record format comparisons
  • Type and value manipulation operations

• Added BENCHMARKS.md documentation with:

  • Usage examples for running different benchmark categories
  • Performance insights and recommendations
  • Guidelines for adding new benchmarks

Benchmark Coverage

• Data sizes: Small (~15B), Medium (~1KB), Large (~100KB)
• Formats: JSON records, CBOR records, CBOR tags, Collections
• Operations: Marshal, Unmarshal, Deserialize, X.509 extensions
• Memory tracking: All benchmarks include allocation reporting

Key Performance Insights

• CBOR tag format is ~2x faster than CBOR record format for monads
• CBOR operations generally outperform JSON equivalents
• Performance scales reasonably with data size
• Memory allocations are well-controlled across all operations

Testing

• All existing tests continue to pass
• New benchmarks execute successfully and provide meaningful metrics
• Memory allocation tracking enabled for optimization insights

Usage

# Run all benchmarks
go test -bench=. -benchmem

# Run specific categories
go test -bench="BenchmarkCMW_Marshal" -benchmem
go test -bench=".*Small.*" -benchmem

Fixes #21