[core] Fix dropping stats in data evolution scan

[leaves12138]

Purpose

DataEvolutionFileStoreScan keeps file statistics during manifest reading because predicate evaluation and per-file column pruning are performed in postFilterManifestEntries.

When neither an input filter nor a read type is configured, postFilterManifestEntriesEnabled() previously returned false. As a result, calling dropStats() had no effect because the post-filtering hook that removes statistics was skipped.

This change:

• always enables post-filtering for data-evolution scans;
• preserves row-id grouping, statistics filtering, and read-type pruning when an input filter or read type is present;
• directly drops statistics when neither an input filter nor a read type is present;
• adds a regression test for dropStats() without a filter or read type.

Tests

• mvn -pl paimon-core -DwildcardSuites=none -Dtest=DataEvolutionTableTest#testDropStatsWithoutFilterOrReadType+testSystemFieldOnlyProjectionIsNotPruned test
• mvn -pl paimon-core -Pfast-build -DwildcardSuites=none -Dtest=DataEvolutionTableTest test (42 tests)