function-after: use input to function as source in error message

[davidhewitt]

Change Summary

Uses the output of the inner validator as the input in the error message for a function-after validator.

This might actually not be a desirable thing to change, so I'm opening this PR to see what CI and integration tests think before going further.

Related issue number

Fix pydantic/pydantic#8126

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 #1278 will not alter performance

_{Comparing dh/function-after-input (dc9007a) with main (1e5e899)}

Summary

✅ 155 untouched benchmarks

[sydney-runkle]

@davidhewitt, would you still like to keep this open as a draft?

[davidhewitt]

We should discuss if this change should be done and either complete or close.

[sydney-runkle]

cc @samuel, we can discuss at oss sync tomorrow.

[davidhewitt]

It looks like the problem here is that models with before validators now output the intermediate state between the model validator and the model fields validator, I think we should be removing that split anyway for performance and handling validators a separate way ideally. So will leave this open with the intent to move forward after those are solved.