refactor Input trait to have single as_python cast for python inputs

[davidhewitt]

Change Summary

Looking at performance of new pydantic-core in pydantic's north star benchmark, I noticed that an easy perf win is to avoid copying Url and MultiHostUrl objects when unnecessary.

At the same time, I refactored the Input trait just a little bit so that all the python-specific methods could be replaced by a single .as_python() call which validators with targeted optimizations could then use.

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 #1241 will not alter performance

_{Comparing dh/url-optimization (64c648b) with main (6399592)}

Summary

✅ 152 untouched benchmarks

[davidhewitt]

It looks like we are missing Url benchmarks, but hopefully this is clear enough....