Rework input buffer to match HDR closer (#79)

## Summary

- Preserve distinct same-action bindings in rollback input frames.
- Add independent command lifetimes with tap and state-scoped hold buffering.
- Detect second shield bindings and consume shield commands for air dodge.
- Fix duplicate keyboard mappings being overwritten.

Reviewed-on: #79
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/input/gamepad.rs

@@ -14,10 +14,13 @@ pub fn sample_gamepad(pad: &Gamepad, input_map: &BaseInputMap) -> FighterInputFr
         match &gamepad_element.binding {
             GamepadBinding::Button(button) => {
                 let pressed = pad.pressed(*button);
+                if let Some(action) = gamepad_element.action.digital_action() {
+                    input_frame
+                        .bindings
+                        .set(action, gamepad_element.binding_slot, pressed);
+                }
                 match gamepad_element.action {
-                    InputMapAction::Jump => input_frame.jump |= pressed,
-                    InputMapAction::Shield => input_frame.shield |= pressed,
-                    InputMapAction::Attack => input_frame.attack |= pressed,
+                    InputMapAction::Jump | InputMapAction::Shield | InputMapAction::Attack => {}
                     // Digital buttons driving movement isn't used by the
                     // default bindings (the stick covers that), but stay
                     // consistent with the keyboard backend if one is added.