refactor(codegen): remove async_include_kwargs config support

[chyroc]

Summary

• Remove api.operation_mappings[].async_include_kwargs from generator config schema and config/generator.yaml.
• Remove Python operation rendering branch for mapping-level async kwargs opt-in.
• Define default behavior as standard kwargs handling without per-operation override.
• Update generator tests to assert async kwargs presence by default path.

Non-overlap With Existing Open PRs

• This PR does not overlap with current open config-removal tracks:
  • force_multiline_request_call
  • response_cast
  • response_unwrap_list_first

Validation

• ./scripts/fmt.sh
• ./scripts/lint.sh
• ./scripts/test.sh (Total coverage: 83.2%)
• ./scripts/build.sh
• ./scripts/gengo.sh
• ./scripts/diffgo.sh (zero diff)
• ./scripts/genpy.sh --output-sdk /tmp/coze-py-qEF1lO --ci-check

Downstream PR

• coze-py PR: chore(py): track async_include_kwargs removal (no sdk diff) coze-py#412