Add ClientOptions.cpuRateLimit

[tomaka]

Adding an option to limit the amount of CPU consumed by smoldot.

Warp syncing a long chain such as Kusama can use a lot of CPU for up to 10-15 seconds, and we'd rather not have a web page or the substrate-connect extension use up an entire CPU for this long, as it tends to cause systems to freeze.
After this change is merged and published, I'd cap the CPU to 50% in substrate-connect.

[mergify]

Automatically approving tomaka's pull requests. This auto-approval will be removed once more maintainers are active.

[github-actions]

twiggy diff report

Difference in .wasm size before and after this pull request.

---

 Delta Bytes │ Item
─────────────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
        +393 ┊ <smoldot_light_wasm::cpu_rate_limiter::CpuRateLimiter<T> as core::future::future::Future>::poll::h129a42f3c0b4c4de
        -201 ┊ smoldot_light_wasm::init::init::{{closure}}::{{closure}}::{{closure}}::h4aab948761687b79
        +201 ┊ smoldot_light_wasm::init::init::{{closure}}::{{closure}}::{{closure}}::hd7e19adb8045aaaf
         +75 ┊ core::ptr::drop_in_place<smoldot_light_wasm::cpu_rate_limiter::CpuRateLimiter<core::future::from_generator::GenFuture<smoldot_light_wasm::init::init<alloc::vec::Vec<futures_util::abortable::AbortHandle>,smoldot_light_wasm::platform::Platform>::{{closure}}>>>::h37d1b6eac73ce75b
         -73 ┊ <smoldot_light_wasm::platform::Platform as smoldot_light_base::Platform>::sleep_until::h004d951d4576a059
         +73 ┊ smoldot_light_wasm::timers::Delay::new_at::h1ceafbbf91a77047
         -64 ┊ core::ptr::drop_in_place<core::future::from_generator::GenFuture<smoldot_light_wasm::init::init<alloc::vec::Vec<futures_util::abortable::AbortHandle>,smoldot_light_wasm::platform::Platform>::{{closure}}>>::h5e689831c5355336
         -54 ┊ smoldot_light_wasm::init::init::{{closure}}::{{closure}}::{{closure}}::hb190226bc087101c
         +54 ┊ smoldot_light_wasm::init::init::{{closure}}::{{closure}}::{{closure}}::hef748433d472c231
         +51 ┊ init
         +42 ┊ smoldot_light_wasm::init::init::{{closure}}::h3739f99282e16c21
         -42 ┊ smoldot_light_wasm::init::init::{{closure}}::h6d729e1d79d0771f
         -11 ┊ type[24]: (i32, i32, i32, i32, i32, i32, i32) -> i32
         +11 ┊ type[25]: (i32, i32, i32, i32, i32, i32, i32) -> i32
          -9 ┊ type[25]: (i32, i32, i32, i32, i32) -> i32
          +9 ┊ type[26]: (i32, i32, i32, i32, i32) -> i32
          +9 ┊ type[39]: (i32, i64, i64, i32, i32) -> i32
          +9 ┊ type[40]: (i32, i64, i32, i32, i32) -> i32
          -9 ┊ type[40]: (i32, i64, i64, i32, i32) -> i32
          -9 ┊ type[41]: (i32, i64, i32, i32, i32) -> i32
          +3 ┊ ... and 34 more.
        +602 ┊ Σ [54 Total Rows]

[melekes]

👍

[melekes]

nitpik: since we're interested in only one arm

Suggested change

	match Future::poll(this.prevent_poll_until.as_mut(), cx) {
	if let Poll::Pending = Future::poll(this.prevent_poll_until.as_mut(), cx) {