What this PR does / why we need it:

Closes #6173

Feature view versioning was introduced in #6101, but version-qualified feature references (e.g. driver_stats@v2:trips_today) only worked with the SQLite online store. All other online stores raised VersionedOnlineReadNotSupported when a versioned ref was used.

This PR adds versioned read/write support to the FAISS online store, following the same pattern as the SQLite reference implementation:

• Write path: when enable_online_feature_view_versioning is enabled, _table_id appends a _v{N} suffix to the in-memory key namespace (e.g. project_driver_stats_v2), routing materialization to the correct versioned index
• Read path: version-qualified lookups (@v2) set projection.version_tag on the feature view before online_read is called; _table_id picks this up and routes to the correct index. projection.version_tag takes priority over current_version_number so explicit version requests are always honoured
• Multi-table support: replaced single class-level _index/_in_memory_store with per-table _indices/_in_memory_stores dicts, so multiple feature views and versions can coexist in memory simultaneously
• Gate: _check_versioned_read_support in online_store.py now allows FaissOnlineStore through

All existing online_read, online_write_batch, retrieve_online_documents, update, and teardown methods are covered since every method resolves its namespace through _table_id.

Which issue(s) this PR fixes:

Part of #2728

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests
• Integration tests
• Manual tests
• Testing is not required for this change

Added 11 unit tests covering _table_id with versioning disabled, projection.version_tag priority over current_version_number, version 0 edge case, no version info fallback, versioned write/read round trips, namespace isolation between versions, missing index handling, and teardown cleanup.

Misc

• Removed "type" from mock config in tests to match FaissOnlineStoreConfig's strict pydantic validation (no extra fields permitted)