SOLR-18039: Add byte-path parity tests for repeated parents.preFilter

[arup-chauhan]

Description

This PR adds parity coverage for SOLR-18039 by validating repeated parents.preFilter behavior on the byte-vector nested KNN paths. The core parser fix was merged in #4139, this follow-up keeps scope narrow to test coverage only.

Context from issue discussion

In SOLR-18039, we fixed repeated parents.preFilter handling and added focused float-path coverage. The remaining gap was parity validation for equivalent byte-vector nested parent-retrieval flows, so this PR closes that gap without extending scope into parser refactoring yet.

Changes

• Added parity tests for repeated parents.preFilter in byte-vector nested parent retrieval.
• Added parity tests for repeated parents.preFilter in byte-vector nested parent retrieval with child preFilter.
• Assertions verify intersection semantics for multiple parent filters, matching the expected behavior already covered on the float path.

Behavior / Safety

• Compatibility: no API or runtime behavior changes.
• Fallback path: existing query execution and filter wiring remain unchanged; this PR only adds coverage.
• Risk boundary: test-only change, focused on regression protection for the byte-vector path.
• Unchanged: parser logic, scoring behavior, request parameter contract, and single-filter behavior from #4139.

Validation

Ran with Java 21 active (jenv/JAVA_HOME set to 21):

• ./gradlew -p solr/core test --tests org.apache.solr.search.join.BlockJoinNestedVectorsQParserTest --tests org.apache.solr.search.join.BlockJoinNestedVectorsParentQParserTest
  Outcome: BUILD SUCCESSFUL (:solr:core:test, 17 tests).
• ./gradlew tidy
  Outcome: BUILD SUCCESSFUL.
• ./gradlew check -x test
  Outcome: BUILD SUCCESSFUL.

Follow-ups

A separate small cleanup PR can still be done to consolidate shared filter-subquery parsing between preFilter and parents.preFilter paths, keeping behavior unchanged.

[arup-chauhan]

Hey @epugh @alessandrobenedetti, as mentioned, here is the quick update:

• Added byte-path parity coverage for repeated parents.preFilter.
• Included both variants: with and without child preFilter.
• Re-ran focused validation locally (test for the two nested-vector suites, tidy, and check -x test) and all passed.

This is test-only follow-up coverage; no parser/runtime behavior changes.