Fix Kitty keyboard protocol and paredit string tracking

Handle printable characters, modifiers, and special keys sent via the
Kitty keyboard protocol (ESC[N;Mu sequences).  Previously only
Shift+Enter was recognized; all other keys were silently dropped,
making it impossible to type characters like " in terminals that use
this protocol (kitty, foot, ghostty, WezTerm, etc.).

Also fix in-string-p and count-unmatched-delimiters where (incf i)
inside (loop for i from ...) had no effect, causing escaped characters
in strings to be tracked incorrectly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>