[core] Do not drop partitions when the system-table partition filter cannot be parsed

[LuciferYang]

Purpose

System tables (t$buckets, t$files, t$fileindexes, t$filekeyranges) render the partition as a single string column and parse a pushed-down equality or IN literal back into a partition spec before pushing it into the snapshot reader. A partition value that contains the ", " separator does not round-trip this format: parsePartitionSpec sees a token count that differs from the number of partition keys and returns null. In that case the Equal branch returned false, which the callers translate into an empty result, so a query filtering for that exact partition silently returned zero rows. The IN branch had the same flaw per literal: it dropped only the unparseable literals from the pushed filter, so their partitions silently vanished from the results.

This treats an unparseable spec the way the range branch already does: skip the partition pushdown and read all partitions, letting the engine re-apply the predicate. For Equal it skips the pushdown when the spec is null; for IN it skips the whole pushdown as soon as any literal fails to parse.

Tests

BucketsTableTest.testBucketsTableWithUnparseablePartitionFilterIsConservative pins that an unparseable equality filter degrades to reading all partitions instead of returning empty.

BucketsTableTest.testBucketsTableWithPartiallyUnparseableInFilterIsConservative pins that a single unparseable IN literal disables the whole pushdown rather than dropping only that literal's partition.

FilesTableTest.testReadWithNotFullPartitionKey is updated from the old empty-result expectation to the conservative all-partitions expectation.

API and Format

No.

Documentation

No.