Validate index rowid position and report corrupt records

[kumarUjjawal]

Description

• Add index rowid-position validation in integrity_check with header-level parsing and a dedicated IndexRecordCorrupt error.
• Avoid brittle index-page assumptions in tests by reading rootpage from sqlite_master.
• Add integration test that corrupts an index record header to ensure detection.

Motivation and context

• Addresses integrity check should check for rowid-not-and-end-of-record violations #5440 by detecting index corruption where rowid is not in the expected position, complementing existing integrity checks.

Closes #5440

Description of AI Usage

Pair programming with codex

[turso-bot]

Please review @jussisaurio

[jussisaurio]

Does SQLite do this using VDBE or specialized non-VDBE code as here?

[kumarUjjawal]

SQLite runs integrity_check through VDBE, but the heavy lifting is done by a dedicated opcode that delegates to non‑VDBE btree integrity code.