Add Dolphin-compatible input expressions and GCPadNew.ini import, DualSense L/R remapping, vibration toggle (#89)

* Add Dolphin-compatible input expressions and GCPadNew.ini import

Rebased onto current main; addresses both CodeRabbit reviews on #89.

- Expression engine matching Dolphin's semantics: doubles rather than
  booleans, 0.5 press threshold, & as min, | as max, and the functions if,
  min, max, clamp, abs, sqrt, pow, sin, cos, tan, deadzone, timer, toggle,
  hold, tap, pulse and smooth. Timing uses a steady clock in seconds, as
  Dolphin does, so a copied expression behaves identically.

- Expressions bind to the GameCube buttons and triggers, combined with the
  existing button mapping rather than replacing it, and are skipped while
  the settings overlay holds input.

- Import reads [GCPadN] from the Dolphin config directory or from
  GCPadNew.ini beside the executable. Stick axes are not expression driven
  and keep their normal mapping.

- Fixes #74: a digital button bound to L or R now reports a fully pulled
  analog trigger, plus a PlayStation preset and a vibration toggle.

Review fixes: config paths round-trip through RuntimeConfigFile::PathToUtf8
and PathFromUtf8 so non-ASCII paths open correctly on Windows, and the
duplicated exists branch is gone; the tap count is clamped before the
unsigned conversion; the expression editor uses resizable storage via
ImGuiInputTextFlags_CallbackResize so a long expression cannot be saved
truncated; clamp bounds are ordered before std::clamp; <cstdlib> is included
for std::strtod; non-finite values are rejected at the evaluator boundary as
well as at the deadzone and timer divisions; and InputBindings::Reload() runs
from InitializeRuntimeSettings rather than the vibration handler.

runtime/tests/test_expr.cpp covers operator precedence, each stateful
function and every case raised in review.

Third review round: smooth() guards NaN as well as infinity so a zero rate
cannot latch a non-finite value in node state; division evaluates both operands
so stateful functions in the left subtree still update when the divisor is zero;
the expression editor clears stale errors when the port changes; and
runtime/tests/test_expr.cpp is registered with CTest as mkw_input_expr_tests,
following the existing test targets.

* Update runtime/src/input_expr.cpp

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* Update runtime/src/input_expr.cpp

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* Update runtime/src/input_expr.cpp

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

README.md

@@ -46,7 +46,9 @@ Press **F10** while the game window has focus:
 - Internal resolution
 - FPS counter
 - Controller assignment for all four ports
-- Full per-controller button mapping
+- Full per-controller button mapping, including the bumpers
+- Dolphin-syntax input expressions and GCPadNew.ini import
+- Controller vibration on/off
 - Volume, instant mute, and the music ducking toggle
 
 Everything you change is saved to `Config.toml` on the spot and restored next launch.
@@ -56,6 +58,16 @@ Controllers are fed to the game as a GameCube controller.
 Mappings are positional (`south`, `east`, `west`, `north`) rather than Xbox-labelled, so the
 same config makes sense on Xbox, PlayStation, Nintendo and generic SDL pads alike, and extra
 inputs like paddles, touchpads and share buttons show up when the hardware reports them.
+
+**Dolphin-compatible input expressions.** 
+Each GameCube control can carry an expression in Dolphin's input syntax, with the same operators
+(`!` `&` `|` `^`) and the same functions (`if`, `min`, `max`, `clamp`, `timer`, `toggle`, `hold`,
+`tap`, `pulse`, `smooth`, `deadzone`), evaluated against the same wall-clock timing. A Dolphin
+`GCPadNew.ini` can be imported directly from the F10 bar. Stick axes are not covered by expressions
+and keep their normal mapping.
+
+**Vibration toggle.** 
+Force feedback can be turned off for every port at once.
 The official Wii U / Switch GameCube adapter (WUP-028) works too; as with Dolphin, on Windows the
 adapter must be switched to the WinUSB driver once (Zadig).