feat: threshold

[leonardoventurini]

This PR adds a new threshold option to control when compression is applied to WebSocket messages. Messages smaller than the threshold will skip compression entirely, which can improve performance by avoiding unnecessary compression overhead on small payloads.

Key Changes

• Added new threshold configuration option (defaults to 0 - always compress)
• Skip compression for messages smaller than threshold size
• Optimized buffer handling for compressed messages using Buffer.allocUnsafe
• Updated GitHub Actions to test only on modern Node.js versions (20+)
• Added comprehensive test coverage for threshold behavior
• Bumped version to 0.1.8
• Renamed package to permessage-deflate2 to avoid conflicts

Why This Matters

Small messages often don't benefit from compression and can actually become larger due to compression overhead. By allowing users to set a minimum size threshold, we can:

1. Improve performance by avoiding unnecessary compression work
2. Reduce CPU usage on high-traffic WebSocket servers
3. Potentially reduce actual message sizes when compression would be counterproductive

Breaking Changes

• Dropped support for Node.js versions before 20
• Package renamed to permessage-deflate2

Usage

deflate = deflate.configure({
  threshold: 100, // Skip compression for messages < 100 bytes
  // ... other options
});