xenia-hid + xenia-debugger: gamepad serializer; debugger fast-skip hook

xenia-hid grows a guest-facing X_INPUT_GAMEPAD writer (big-endian on
the wire, host-neutral GamepadState in memory) so XamInputGetState in
the kernel and the UI input thread share one POD snapshot type. Adds
the GUIDE button flag.

xenia-debugger gains Debugger::wants_hooks(), a single-branch fast
path the hot interpreter loop checks to skip the pre_step/post_step
HashMap+match work when the debugger is in cold-run mode (no bps, no
trace, StepMode::Run, not paused). Part of the Tier-3 perf landing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/xenia-hid/Cargo.toml

@@ -6,5 +6,6 @@ license.workspace = true
 
 [dependencies]
 xenia-types = { workspace = true }
+xenia-memory = { workspace = true }
 tracing = { workspace = true }
 thiserror = { workspace = true }