The type of the function / 函数的类型
The async function to wrap. / 要包装的异步函数
The maximum number of concurrent executions. / 最大并发数
The wrapped async function. / 包装后的异步函数
This is a call-site limiter: every invocation of the returned function shares
the same concurrency budget, no matter where it is called from. Unlike
promiseParallel, it does not collect a batch of tasks, and it has no
fast-fail behavior — when combined with Promise.all, every call is eventually
executed even if some of them reject. Under the hood it is built on
Semaphore: it takes the synchronous Semaphore.tryAcquire fast
path while permits are free, avoiding an extra Promise allocation and microtask
hop, and only falls back to the asynchronous Semaphore.acquire once the
permits are exhausted.
这是调用点限流器：无论从何处调用，返回函数的每次调用都共享同一个并发预算。
与 promiseParallel 不同，它不收集一批任务，也没有 fast-fail 行为——
与 Promise.all 组合时，即使部分调用失败，所有调用最终也都会执行。
底层基于 Semaphore 实现：当仍有空闲许可时优先走同步的
Semaphore.tryAcquire 快路径，避免额外的 Promise 分配与微任务调度，
仅在许可耗尽时才回退到异步的 Semaphore.acquire。
const limitedFetch = limitAsync(async (url) => {
return await fetch(url);
}, 3);
// Only 3 fetches will run concurrently
const urls = ['url1', 'url2', 'url3', 'url4', 'url5'];
await Promise.all(urls.map(url => limitedFetch(url)));
Wraps an async function to limit the number of concurrent executions.
This function creates a wrapper around an async callback that ensures at most
concurrencynumber of executions can run simultaneously. Additional calls will wait until a slot becomes available.将异步函数包装起来以限制并发执行的数量。
此函数创建一个异步回调的包装器，确保最多只有
concurrency个执行可以同时运行。 额外的调用将等待直到有可用的执行槽位。