[nfc] STW refactor and cleanup

[fhanau]

No description provided.

[codspeed-hq]

CodSpeed Performance Report

Merging #5377 will improve performances by ×2

_{Comparing felix/102025-stw-cleanup (1550a46) with main (e040ae7)}

Summary

⚡ 1 improvement
✅ 27 untouched
⏩ 9 skipped¹

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	Encode_OneByte_1024[0/1/1024]	2.4 s	1.2 s	×2

Footnotes

1. 9 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. ↩