Add LPAREN, RPAREN, COMMA token types to the scanner

Extends the vec0 tokenizer to recognize '(', ')', and ',' as
single-character tokens, preparing for DiskANN index option parsing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/sqlite-vec-internal.h

@@ -23,6 +23,9 @@ enum Vec0TokenType {
   TOKEN_TYPE_RBRACKET = 3,
   TOKEN_TYPE_PLUS = 4,
   TOKEN_TYPE_EQ = 5,
+  TOKEN_TYPE_LPAREN = 6,
+  TOKEN_TYPE_RPAREN = 7,
+  TOKEN_TYPE_COMMA = 8,
 };
 
 #define VEC0_TOKEN_RESULT_EOF   1