feat: add per-request compression toggles

[KokaKiwi]

Checklist

• I have read the Contributor Guide
• I have read and agree to the Code of Conduct
• I have added a description of my changes and why I'd like them included in the section below

Description of Changes

Adds tool_result_trimming, tool_surface_reduction and output_brevity to InputObject (and the dict input), so a caller can switch each compression strategy on or off for one request.

• Wire format: send, streaming included, sends each field that is set as its X-Edgee-Compression-* header. Unset fields send nothing, so the API key setting applies. With dict input, only real bool values count. None of them go into the request body.
• Deprecation: setting compression_model now emits a DeprecationWarning. It still works, and the gateway reads any value as "trimming on".

example/compression.py now sends a tool call with a long ls -la result, since tool results are what trimming shortens.

Covered by pytest tests, and checked against a local gateway, where the provider's input token counts moved as expected for each toggle.

Related Issues

Related to EDGEE-1640