Add limitConcurrency function

[aleclarson]

Combine a Semaphore object with an async function to limit its concurrency (i.e. the maximum number of unresolved promises from the wrapped function, at any given time).

import { Semaphore } from 'radashi'

export function limitConcurrency<T extends (...args: any[]) => Promise<any>>(
  concurrency: number,
  fn: T,
) {
  const semaphore = new Semaphore(concurrency)
  return async (...args: Parameters<T>) => {
    const permit = await semaphore.acquire()
    try {
      return await fn(...args)
    } finally {
      permit.release()
    }
  }
}