fix: Share reqwest HTTP clients

[tmathern]

Changes in this pull request

• Share reqwest clients (avoid client recreation and related memory consumption).

Checklist

• This PR represents a single feature, fix, or change.
• All applicable changes have been documented.
• Any TO DO items (or similar) have been entered as GitHub issues and the link to that issue has been included in a comment.

[codspeed-hq]

Merging this PR will not alter performance

✅ 30 untouched benchmarks
⏩ 64 skipped benchmarks¹

---

_{Comparing mathern/pool-reqwest (8bdf883) with main (87243f6)}

Footnotes

1. 64 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩