fix(validation): remove repeat paths in markers

[ricokahler]

Description

This PR fixes a regression in the validation refactor.

When I did the refactor, I didn't understand that the path inside of ValidationError was supposed to be relative to the current value (for array and object values).

I was previously incorrectly appending item-level paths. The refactor passes the validation context around more freely so the applyPathPrefix function was redundant.

What to review

• Try out all validation and especially try validation with items that create markers to nested value inside the current value (e.g. array items and uniqueness, array items and Rule.valid values, custom block editors).
• Review the new tests. I mocked a bit more and to re-create the error. This was known to happen with slugs.

Notes for release

Fixes regression in @sanity/validation regarding incorrect marker paths (#2713). This fixes focus issues in the validation list.

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perf-studio – ./

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test-studio – ./

🔍 Inspect: https://vercel.com/sanity-io/test-studio/9svevBgvWzwxF6qSXbgPMnPrB6NJ
✅ Preview: https://test-studio-git-fix-ch10895repeat-paths-in-markers.sanity.build