Support parsing doubly quoted strings as identifiers

[garnacho]

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.