Timers fixes

[id-ilych]

DISCLAIMER:
I have no expertise in the project and no expertise in rust, so it is rather experiment/exploration/playground.
I did not bother checking timers' specification, but it should be fine given the current goals.
Also, the implementation currently stores callback function in JS' globals which is not ideal, but I haven't found a way to do it on rust level (yet).

• Don't use global variable for timers queue
  It seems, timer tests are not flaky now
• Refine the code
• Add support for function callbacks (and related test to cover)

Description of the change

Why am I making this change?

Checklist

• I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli and javy-plugin do not require updating CHANGELOG files.
• I've updated the relevant crate versions if necessary. Versioning policy for library crates
• I've updated documentation including crate documentation if necessary.

[Copilot]

Pull Request Overview

This PR replaces the global timer queue with a per-Runtime timer manager and introduces a new TimerQueue implementation.

• Refactor Runtime to hold an Option<TimersRuntime> instead of a global flag and functions
• Update Runtime methods (build_from_config, resolve_pending_jobs, has_pending_jobs) to use the new TimersRuntime API
• Add a heap-backed TimerQueue with basic operations and tests

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
crates/javy/src/runtime.rs	Refactored timer support from globals to Option<TimersRuntime> and removed the old flag and functions
crates/javy/src/apis/timers/queue.rs	Added TimerQueue implementation with heap logic and initial tests

Comments suppressed due to low confidence (3)

crates/javy/src/runtime.rs:214

• Removing the public has_timers_enabled method is a breaking API change; consider reintroducing it as a deprecated alias or updating all callers.

pub fn has_timers_enabled(&self) -> bool {

crates/javy/src/apis/timers/queue.rs:89

• [nitpick] There are no tests covering get_expired_timers. Add unit tests to verify that timers fire at the correct time and repeating timers are re-enqueued as expected.

pub fn get_expired_timers(&mut self) -> Vec<Timer> {

crates/javy/src/apis/timers/queue.rs:9

• [nitpick] The Function variant in TimerCallback is ambiguous; consider renaming it to something more descriptive (e.g., FunctionRef or CallbackFn).

Function,

[Copilot]

Calling .retain on a BinaryHeap breaks its internal heap invariant. Instead, filter elements and rebuild the heap (e.g., BinaryHeap::from(filtered_vec)), or use a data structure that supports efficient removal.

Suggested change

	self.timers.retain(|timer| timer.id != timer_id);
	let filtered_timers: Vec<_> = self.timers.drain().filter(|timer| timer.id != timer_id).collect();
	self.timers = BinaryHeap::from(filtered_timers);

[id-ilych]

1. I see no such comments in the docs https://doc.rust-lang.org/std/collections/struct.BinaryHeap.html#method.retain
2. They even fixed potential invariant breakage in case of a panic Rebuild BinaryHeap on unwind from retain rust-lang/rust#106918

From that I conclude that the comment is misleading.