Implement xRename for vec0 virtual table (fixes #43)

Enables ALTER TABLE RENAME on vec0 tables by renaming all shadow tables
(info, rowids, chunks, auxiliary, vector_chunks, metadata, rescore,
diskann, ivf) and updating cached names and prepared statements.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>