Reapply "Fix `JSClosure` leak (#240)"

[kateinoigakukun]

Seems like something wrong is happening in https://github.com/swiftwasm/JavaScriptKit/actions/runs/8659623850. I need stress test this before re-landing this.

This reverts commit 8780e5f005933c1d83d74942a14f78c1fc03e499.

[github-actions[bot]]

Time Change: +114ms (1%)

Total Time: 9,319ms

Test name	Duration	Change
Serialization/JavaScript function call through Wasm import	19ms	-4ms (19%)	👏

View Unchanged

| Test name | Duration | Change | | :--- | :---: | :---: | | Serialization/JavaScript function call through Wasm import with int | 15ms | -1ms | | Serialization/JavaScript function call from Swift | 99ms | +2ms (1%) | | Serialization/Swift Int to JavaScript with assignment | 330ms | +9ms (2%) | | Serialization/Swift Int to JavaScript with call | 939ms | +8ms (0%) | | Serialization/JavaScript Number to Swift Int | 303ms | -1ms | | Serialization/Swift String to JavaScript with assignment | 383ms | -0ms | | Serialization/Swift String to JavaScript with call | 976ms | -7ms (0%) | | Serialization/JavaScript String to Swift String | 3,622ms | +96ms (2%) | | Object heap/Increment and decrement RC | 2,620ms | +12ms (0%) |

View Baselines

| Test name | Duration | | :--- | :---: | | Serialization/Call JavaScript function directly | 3ms | | Serialization/Assign JavaScript number directly | 2ms | | Serialization/Call with JavaScript number directly | 3ms | | Serialization/Write JavaScript string directly | 3ms | | Serialization/Call with JavaScript string directly | 2ms |