Return early from concurrency() and rate_limit() without limit names

[abrookins]

If a user calls concurrency() or rate_limit() and passes a None value or an empty collection, return early to avoid making unnecessary API requests.

Fixes #14786

Checklist

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  • If no issue exists and your change is not a small fix, please create an issue first.
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[codspeed-hq]

CodSpeed Performance Report

Merging #14789 will not alter performance

_{Comparing issue-14786 (eab1118) with main (b3c9a71)}

Summary

✅ 5 untouched benchmarks

[cicdw]

beautiful