m: Remove once_cell dependency

Removes the once_cell dependency, instead using std::sync::OnceLock and a
minimal polyfill for std::sync::LazyLock, which may be stabilized soon
(see rust-lang/rust#121377).

This should not require a bump in MSRV, as OnceLock was stabilized in 1.70,
which this crate is using.

src/platform_impl/android/mod.rs

@@ -12,12 +12,12 @@ use std::{
     time::{Duration, Instant},
 };
 
+use crate::utils::Lazy;
 use android_activity::input::{InputEvent, KeyAction, Keycode, MotionAction};
 use android_activity::{
     AndroidApp, AndroidAppWaker, ConfigurationRef, InputStatus, MainEvent, Rect,
 };
 use log::{debug, trace, warn};
-use once_cell::sync::Lazy;
 
 use crate::{
     cursor::Cursor,