Support parsing doubly quoted strings as identifiers

Per https://www.sqlite.org/lang_keywords.html, SQLite supports
identifiers expressed as strings surrounded between double quotes:

    $ sqlite3
    SQLite version 3.52.0 2026-03-06 16:01:44
    Enter ".help" for usage hints.
    Connected to a transient in-memory database.
    Use ".open FILENAME" to reopen on a persistent database.
    sqlite> create table a("oh,boy!" TEXT);
    sqlite> pragma table_info(a);
    ╭─────┬─────────┬──────┬─────────┬────────────┬────╮
    │ cid │  name   │ type │ notnull │ dflt_value │ pk │
    ╞═════╪═════════╪══════╪═════════╪════════════╪════╡
    │   0 │ oh,boy! │ TEXT │       0 │ NULL       │  0 │
    ╰─────┴─────────┴──────┴─────────┴────────────┴────╯

When identifiers are parsed as such, no escaping applies, i.e.
backslashes don't affect the next character:

    sqlite> create table b("oh\tno\" TEXT);
    sqlite> pragma table_info(b);
    ╭─────┬─────────┬──────┬─────────┬────────────┬────╮
    │ cid │  name   │ type │ notnull │ dflt_value │ pk │
    ╞═════╪═════════╪══════╪═════════╪════════════╪════╡
    │   0 │ oh\tno\ │ TEXT │       0 │ NULL       │  0 │
    ╰─────┴─────────┴──────┴─────────┴────────────┴────╯

Make sqlite-vec internal scanner handle these identifiers, so
that the column names in a vec0 virtual table may have the same
(reduced) limitations as any other SQLite table.

Note: SQLite also implements similar support for single quoted
strings to be handled as identifiers. This is done for compatibility
with other SQL implementations rather than standard conformance,
so it's perhaps a bit more dubious to support.

Author: garnacho

sqlite-vec.c

@@ -2157,6 +2157,17 @@ int vec0_token_next(char *start, char *end, struct Vec0Token *out) {
       out->end = ptr;
       out->token_type = TOKEN_TYPE_IDENTIFIER;
       return VEC0_TOKEN_RESULT_SOME;
+    } else if (curr == '"') {
+      char *start = ptr;
+      int match = 0;
+      do {
+        match = ptr > start && (*ptr == '"');
+        ptr++;
+      } while (ptr < end && !match);
+      out->start = start;
+      out->end = ptr;
+      out->token_type = TOKEN_TYPE_IDENTIFIER;
+      return VEC0_TOKEN_RESULT_SOME;
     } else if (is_digit(curr)) {
       char *start = ptr;
       while (ptr < end && (is_digit(*ptr))) {