Add MiniMax provider support to Mobile-Agent-E

[octo-patch]

Summary

• Add MiniMax as a configurable Mobile-Agent-E backbone with MiniMax-M3 and MiniMax-M2.7.
• Support global and China endpoints through OpenAI-compatible and Anthropic-compatible protocols using one base URL setting.
• Track regional, context-tier, service-tier, and cache usage costs, and document the supported configuration.
• Add focused tests for endpoint request construction, protocol payloads, and pricing tiers.

Testing

• python3 -m unittest discover -s Mobile-Agent-E/tests -p 'test_*.py' -v
• python3 -m py_compile Mobile-Agent-E/MobileAgentE/api.py Mobile-Agent-E/inference_agent_E.py Mobile-Agent-E/tests/test_api.py
• git diff --check