[codex] Expand local-workers grouped aggregate hot path

[ashione]

Summary

• expand the local-workers credit hot path from fixed window/key SUM/COUNT into generic grouped aggregates
• keep the public execution modes as single-process and local-workers
• expose Python stream SQL options and add Python e2e coverage for the new path and zero-worker fallback semantics

Validation

• bazel test //:stream_actor_credit_test
• bazel test //:stream_strategy_explain_test
• bazel test //:sql_regression_test
• bazel test //:stream_runtime_test
• bazel test //:core_regression
• bazel test --repo_env=VELARIA_PYTHON_BIN=/Library/Crypt/Python.framework/Versions/3.8/bin/python3 //python_api:streaming_v05_test