test: create initial mock tty for testing

This is very primitive right now, but we'll add tests.  This MockTty
is, wait for it, a terminal emulator! (or simulator).

More tests will be added, and a full parser for incoming commands,
as well as responses from the terminal to queries made.  We will also
support injecting commands for the purposes of simulation.

fix: ctrl-J is reported as KeyCR/KeyEnter on legacy terminals (fixes #…

…911)

fix: fix various errors in parser - especially nested win32-input-mode

This seems to fix things quite nicely for WezTerm regardless of
running remotely or locally on Windows, or on macOS.  The goofy
nesting level only needs to be done when dealing with nesting, and
we can be reasonably sure that all content requiring the extra
parse pass comes together and is complete (and is generally only
required for non-keyboard data.)

fix: fix terminal key protocol selection logic

This change was merged to main already, but we need it for v2 as
well.  This fixes things for both WezTerm and for win32-input-mode
in general.

fix(windows): remove incorrect +1 from console dimension calculations

The Windows Console API already returns the correct dimensions (0-based
coordinates)

Closes #889

fix(windows): remove incorrect +1 from console dimension calculations

The Windows Console API already returns the correct dimensions (0-based
coordinates)

Closes #889

(cherry picked from commit fd4d7a8)

CodeRabbit Generated Unit Tests: Add comprehensive unit tests for inp…

…ut.go null-byte handling

fix(docs): fix links

fix: rxvt key handling enhancments

rxvt uses non-ECMA compliant escapes (not valid CSI sequences) for
some key sequences, as it uses '$' as a final character in some cases.
This adds support for shift modified keys for insert, delete, home, end,
pageup, page down, as well as control-shift variants.

feat: Desktop notifications (fixes #499)

This only adds support for OSC 777 terminals, but that seems to
include ghostty, wezterm, and probably a number of others.
A demo is included.