[Feature Request] Add support for Python 3.14 t-strings

[davepeck]

Python 3.14 adds a new t-string literal syntax and ships in just a few weeks.

The good news is that it's easy to support: it shares the same syntax as f-strings. Anywhere you can prefix a string with an f or F, you can also prefix it with a t or T in Python 3.14. Hopefully this makes updating the grammar straightforward.