gh-139742: Add support for Python 3.14 t-string prefixes in IDLE colorizer and tests (#139756)

Add 't' prefix to colorizer.py stringprefix regex to support Python 3.14 template strings.
Add t prefixes to test_colorizer.py source test text and adjust line numbers on test methods.
---------

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>
Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>