Refactor guarded reads with ValidatedReader

[zanieb]

Amends the implementation in #20099 to use a reusable builder pattern instead of a special "utf-8 with prefix validation" function.

[astral-sh-bot]

uv test inventory changes

This PR changes the tests when compared with the latest zsol/list-scripts baseline.

• Added tests: 1
• Removed tests: 7
• Changed suites: 5

uv-fs: +1 / -0

Added:

• uv-fs::read::tests::reads_without_utf_8_validation

Removed: none

uv-installer: +0 / -1

Added: none

Removed:

• uv-installer::site_packages::tests::sorted_dist_like_paths_filters_and_sorts

uv-workspace: +0 / -2

Added: none

Removed:

• uv-workspace::pyproject_mut::test::add_index_preserves_format_when_windows_path_unchanged
• uv-workspace::pyproject_mut::test::add_index_syncs_format_on_url_update

uv::it: +0 / -1

Added: none

Removed:

• uv::it::network::retry_read_timeout_python_downloads_json

uv::project: +0 / -3

Added: none

Removed:

• uv::project::edit::add_index_with_existing_relative_path_in_script
• uv::project::export::pep_751_no_packages
• uv::project::export::requirements_txt_conditional_transitive_extra

[codspeed-hq]

Merging this PR will not alter performance

✅ 22 untouched benchmarks

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_{Comparing zb/validated-reader-builder (9b38b94) with main (93ae523)}