Fix UnixUserRecord shell field type from string to path

[Peter-The-Great]

Made sure to change the field type of shell in UnixUserRecord from string to path. I also added a unit test, with a sanity check to make sure that the operation goes correctly as stated.

Closes #900.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #1260 will not alter performance

_{Comparing Peter-The-Great:fix/markusershellpath (9484751) with main (34557ac)[^unexpected-base]} [^unexpected-base]: No successful run was found on main (b4473a6) during the generation of this report, so 34557ac was used instead as the comparison base. There might be some changes unrelated to this pull request in this report.

Summary

✅ 8 untouched benchmarks

[Peter-The-Great]

Sure, I finally have the time.

Still working on it.