feat: concurrency mode

[Aslemammad]

Resolves #76

By default runConcurrently runs the different tasks concurrently at the same time! But runConcurrently(number, "task") would run the iterations of each task concurrently at the same time!

Concurrency

• When mode is set to null (default), concurrency is disabled.
• When mode is set to 'task', each task's iterations (calls of a task function) run concurrently.
• When mode is set to 'bench', different tasks within the bench run concurrently

// options way (recommended)
bench.threshold = 10 // The maximum number of concurrent tasks to run. Defaults to Infinity.
bench.concurrency = "task" // The concurrency mode to determine how tasks are run.  
// await bench.warmup()
await bench.run()

// standalone method way
await bench.runConcurrently(10, "task") // with runConcurrently, mode is set to 'bench' by default

[github-actions]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
dist/index.js	3.36 KB (+29.68% 🔺)	68 ms (+29.68% 🔺)	16 ms (+581.34% 🔺)	83 ms
dist/index.cjs	3.61 KB (+27.08% 🔺)	73 ms (+27.08% 🔺)	19 ms (+324.61% 🔺)	91 ms