feat: add MiniMax model provider

[octo-patch]

Reason: add target provider/model to existing provider registry

Summary

• register MiniMax model routing and credential catalog support
• route MiniMax Anthropic Messages and OpenAI Responses requests to region-aware compatibility endpoints
• add MiniMax-M3 and MiniMax-M2.7 examples with global and China base URLs
• cover both protocols with request-capture tests

Checks

• cargo fmt --check
• cargo test
• cargo check --all-targets

[octo-patch]

I fixed the SDK structure test to stay within the repository code-size limit and pushed a new commit. I ran cargo fmt --all --check, cargo check --all-targets --locked, cargo clippy --all-targets --locked -- -D warnings, cargo test --locked, and python3 scripts/check_code_size.py.