[core] Honor query-level search-mode overrides

[CrownChu]

What is the purpose of the change?

DataEvolutionVectorScan reads search-mode settings directly from table options, so query-level overrides supplied by the query builder are ignored. This prevents callers from overriding vector or scalar index search behavior for an individual query.

Brief change log

• Build effective options by applying table options first and query options second.
• Use the effective options for both vector-index and scalar-index search modes.
• Add regression coverage proving that a query-level scalar full-search override restores fallback rows when the table default is fast mode.

Verifying this change

mvn -pl paimon-core -am -DskipITs -Dfast \
  -Dtest=VectorSearchBuilderTest#testFastScalarModePartialPreFilterOnlyUsesIndexedRows \
  -Dsurefire.failIfNoSpecifiedTests=false test

Result: the focused regression test passed. Spotless and Checkstyle also passed.