fix: propagate api_budget to parent streams in substream partition routers

Summary

This PR fixes issue airbytehq/oncall#9874 where api_budget configuration was not being applied to parent streams in parent-child stream scenarios, causing 403 rate limit errors.

Root Cause: When create_parent_stream_config_with_substream_wrapper creates a new ModelToComponentFactory instance for handling parent streams in SubstreamPartitionRouter scenarios, the global _api_budget was not being propagated to the new factory instance.

Fix: Added one line to propagate _api_budget from the parent factory to the substream factory, ensuring parent streams respect the same rate limiting configuration as child streams.

Changed Files:

• airbyte_cdk/sources/declarative/parsers/model_to_component_factory.py (2 lines added)

Review & Testing Checklist for Human

This is a targeted fix with minimal code changes, but has medium confidence due to limited test coverage:

• Critical: Test with an actual connector that uses substream partition routers (e.g., On24 source or similar) and verify that parent streams now respect api_budget configuration and no longer hit 403 rate limit errors
• Verify that the existing test suite passes (pytest unit_tests/sources/declarative/parsers/test_model_to_component_factory.py)
• Review that propagating _api_budget via direct field assignment is the correct approach (consistent with how other factory state is handled)
• Check for any edge cases where this propagation could cause unintended behavior

Test Plan Recommendation

To verify the fix end-to-end:

1. Create or use an existing declarative connector with:
   • Global api_budget configuration with a low rate limit (e.g., 29 requests/minute)
   • A child stream with SubstreamPartitionRouter that depends on a parent stream
2. Run a sync and verify:
   • Parent stream respects the rate limit (should not exceed configured limit)
   • No 403 errors occur from exceeding API rate limits
   • Child stream correctly processes records from parent stream

Notes

• Test Coverage Limitation: I attempted to add a unit test specifically for this scenario but encountered difficulties getting the test manifest structured correctly after 3 attempts. The fix passes existing tests (test_create_substream_partition_router and test_api_budget), but explicit test coverage for api_budget propagation to parent streams would be beneficial.
• Related Issue: This is related to airbytehq/airbyte#53129 - "[low-code] Back-off strategy is not applied to parent streams"
• Customer Impact: Tier 0/ICP-A customer (Invesco) experiencing this with On24 source v6.61.6

Session: https://app.devin.ai/sessions/14c6cca74bb741e782dfb81d6e2a2c50
Requested by: unknown () via /ai-fix command on oncall issue #9874