Use ONLY for CTID snapshot queries to exclude inherited child rows

[kvch]

Problem

The CTID page-range data snapshot uses SELECT * FROM <table> WHERE ctid BETWEEN ... and SELECT MAX(ctid) FROM <table>. For a legacy-inheritance parent table (CREATE TABLE ... INHERITS), these implicitly span the parent plus all child heaps, so CTIDs aren't unique to the parent's storage: page ranges overlap and child rows get copied through the parent (and again when the child is snapshotted on its own).

Fix

Add ONLY to the page-range and max-CTID queries so each snapshot is confined to the selected table's own heap, matching pgstream's per-table snapshot model.

Note: this is a no-op for plain tables and leaf partitions, and does not affect declaratively partitioned parents (relkind='p'), which are already excluded from this path by the relkind='r' filter in getTableInfo.

Testing

• Unit: TestSnapshotQueriesDoNotIncludeInheritedRows
• Integration: Test_SnapshotToPostgres_SelectedParentTableDoesNotCopyInheritedRows
• go test ./pkg/snapshot/generator/postgres/data/...

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Cherry-picked from @danddanddand (fix/snapshot-only-table-pages).

[github-actions]

Merging this branch will not change overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/xataio/pgstream/pkg/snapshot/generator/postgres/data	78.48% (ø)
github.com/xataio/pgstream/pkg/stream/integration	0.00% (ø)

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/xataio/pgstream/pkg/snapshot/generator/postgres/data/pg_snapshot_generator.go	84.47% (ø)	206	174	32

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/xataio/pgstream/pkg/snapshot/generator/postgres/data/pg_snapshot_generator_test.go
• github.com/xataio/pgstream/pkg/stream/integration/snapshot_pg_integration_test.go