feat: filter GTFS feeds by status

[mackenziereading19]

Summary

Adds support for filtering /v1/gtfs_feeds by the existing status query parameter.

This reuses the shared status contract already used by /v1/feeds, including:

• active
• deprecated
• inactive
• development
• future

The future status was already present in the API schema/documentation, so no new status value was required.

Implementation

• expose the existing status parameter on /v1/gtfs_feeds;
• pass the value through FeedsApiImpl.get_gtfs_feeds;
• add status filtering to GtfsFeedFilter;
• pass the filter through get_gtfs_feeds_query;
• add integration coverage for filtering GTFS feeds by active status.

Verification

Local verification on Python 3.11, matching CI:

• focused status-filter regression: 1 passed;
• baseline + regression: 2 passed;
• api/tests/integration/test_feeds_api.py: 96 passed;
• flake8: passed;
• Black check: passed.

Closes #1675