fix: update MiniMax model metadata and endpoints

[octo-patch]

Reason: add target provider/model to existing provider registry

Summary

• Correct MiniMax-M3 and MiniMax-M2.7 context metadata.
• Preserve MiniMax-M3 standard and priority pricing across both input-length tiers, including cache-read rates.
• Respect regional base URL overrides and document both compatible API formats.
• Route MiniMax usage accounting through the tier-aware callback.

This clean replacement is based on the latest main and supersedes #1101.

Test plan

• .venv/bin/python -m pytest tests/test_minimax_models.py
• The complete deterministic test list from .github/workflows/test-suite.yml (66 passed)
• .venv/bin/ruff check on all changed Python files
• .venv/bin/black --check on all changed Python files
• Mock-transport request capture for every documented regional endpoint

[VinciGit00]

remove the file