python-sdk: generated type foundation (all v2 schemas)

[shaqayeq-oai]

Summary

Foundation PR only (base for PR #3).

This PR contains the SDK runtime foundation and generated artifacts:

• pinned runtime binary in sdk/python/bin/ (codex or codex.exe by platform)
• single maintenance script: sdk/python/scripts/update_sdk_artifacts.py
• generated protocol/types artifacts under:
  • sdk/python/src/codex_app_server/generated/protocol_types.py
  • sdk/python/src/codex_app_server/generated/schema_types.py
  • sdk/python/src/codex_app_server/generated/v2_all/*
• generation-contract test wiring (tests/test_contract_generation.py)

Release asset behavior

update_sdk_artifacts.py now:

• selects latest release by channel (--channel stable|alpha)
• resolves the correct asset for current OS/arch
• extracts platform binary (codex on macOS/Linux, codex.exe on Windows)
• keeps runtime on single pinned binary source in sdk/python/bin/

Scope boundary

• ✅ PR (cleanup) add link to https://cookbook.openai.com for apply_patch and minor tidy up #2 = binary + generation pipeline + generated types foundation
• ❌ PR (cleanup) add link to https://cookbook.openai.com for apply_patch and minor tidy up #2 does not include examples/integration logic polish (that is PR move all tests under tests/ #3)

Validation

• Ran: python scripts/update_sdk_artifacts.py --channel stable
• Regenerated and committed resulting generated artifacts
• Local tests pass on branch