Initial pass at metadata filtering

TODO

@@ -16,3 +16,13 @@
 - drop aux shadow table on xDestroy
 - perf: INSERT stmt should be cached on vec0_vtab
 - perf: LEFT JOIN aux table to rowids query in vec0_cursor for rowid/point stmts, to avoid N lookup queries
+
+# metadata filtering
+
+- boolean value handling
+- DELETE and UPDATE support
+- large strings
+- date/datetime
+- `v in (...)` handling
+- remaining TODO items
+- dictionary encoding?