refactor LookupKey logic to reduce redundancy

[davidhewitt]

Change Summary

Precursor to #1620, which is itself a precursor to moving forward with pydantic/jiter#184

The idea here is that the LookupPath stuff contains a bunch of redundant String and Py<PyString> values. I work these away.

I also removed Clone implementation at the same time, which gets us closer to removing PyO3's py-clone feature.

Related issue number

N/A

Checklist

• Unit tests for the changes exist
• Documentation reflects the changes where applicable
• Pydantic tests pass with this pydantic-core (except for expected changes)
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

[codspeed-hq]

CodSpeed Performance Report

Merging #1635 will not alter performance

_{Comparing dh/lookup-path-refactor (d6938ef) with main (7da4798)}

Summary

✅ 157 untouched benchmarks

[davidhewitt]

Integration test failure is due to #1585, so not a concern.

Given there are no perf concerns nor behavioural changes, I'm just going to merge this and move on.