feat(zgfx): ZGFX (RDP8) compression support for server-side encoding

[glamberson]

Summary

Implementation of ZGFX compression for server-side EGFX encoding is ready for submission. This adds the encoding counterpart to the existing decompressor in ironrdp-graphics.

What's Implemented

• LZ77-variant compressor with O(1) hash table lookup
• Huffman token encoding per MS-RDPEGFX specification
• Segment wrapper for single and multipart framing
• Round-trip compatible with existing Decompressor
• 46 tests covering compression, wrapping, and edge cases

Context

This addresses work noted as incomplete in PR #648 (elmarco's WIP GFX) and supports the server-side EGFX implementation in PR #1057. The compression enables efficient bandwidth usage for EGFX PDU transmission.

Submission Options

I have this ready to submit and wanted to coordinate on preferred approach:

1. Single PR - compressor.rs + wrapper.rs together
2. Split PRs - wrapper.rs first (simpler), compressor.rs second

Layer Considerations

Current implementation places compression alongside the existing decompressor in ironrdp-graphics. An alternative would be a dedicated compression crate, but this deviates from current structure.

Related

• Issue Add GFX ([MS-RDPEGFX]) support  #427 - EGFX feature request
• PR WIP: Add GFX ([MS-RDPEGFX]) support  #648 - Lists ZGFX compression as incomplete
• PR feat(egfx): add MS-RDPEGFX Graphics Pipeline Extension #1057 - EGFX server implementation