fix: continue validating trips after circular trip

[al07mdd]

Summary

Fixes #2203. TripHeadsignValidator compared circular-trip stop IDs by object identity and returned from the entire validation method when a loop was found. This change compares IDs by value and skips only the circular trip, so later trips are still checked.

Expected behavior

Two synthetic regression tests cover equal stop IDs held in distinct String objects and an eligible trip after a circular trip. Both tests failed against the base code and pass with this fix. Notice counts may increase for trips that were previously skipped; results across this validator change should be treated as different validation methods.

Checks

• Full gradlew test --offline --no-daemon passed on JDK 17.
• The changed Java files are formatted.
• No documentation change is needed for this internal validator fix.
• Related issue linked; title follows Conventional Commits.
• Screenshots are not applicable to a validator rule; the synthetic tests demonstrate the behavior.

[CLAassistant]

All committers have signed the CLA.