Fix vector index reuse after indexed column update

[3em0]

Fixes #54

Summary

• mark vector-indexed columns updated by mutation commands for vector index rebuild
• skip hardlinking old vector index files when an indexed vector column must be rebuilt
• add a vector search regression test that rejects ALTER UPDATE on an indexed vector column

Testing

• static source check that UPDATE mutations populate the vector-index rebuild set and skip old .vidx files
• git diff --check -- src/Storages/MergeTree/MutateTask.cpp tests/queries/2_vector_search/00042_mqvs_update_vector_indexed_column.sql tests/queries/2_vector_search/00042_mqvs_update_vector_indexed_column.reference

I could not run the SQL test locally because this environment does not have clickhouse-server/clickhouse-client or Docker installed.