[IlyaKhalafi]

Description

This PR fixes list and item schemas being tied to the same custom name. With this, submodel_name lets each have its own name while keeping existing naming defaults.

Motivation and Context

Fixes #1728.

How Has This Been Tested?

make check and 55 focused tests passed. The full SQLite suite passed with 1,982 tests, 149 skips and two expected failures. Tests used the bundled pytz timezone data because the host lacks US/Central, which also fails on unchanged upstream.

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codspeed]

Merging this PR will not alter performance

⚠️ 21 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• test_values_list_100_rows
• test_update_few_fields_with_save
• test_update_many_fields_with_save
• test_hydrate_100_rows_many_fields
• test_update_few_fields_with_update
• test_filter_few_fields
• test_create_many_fields
• test_create_few_fields
• test_hydrate_100_rows_few_fields
• test_bulk_create_many_fields
• …and 11 more

✅ 24 untouched benchmarks

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_{Comparing IlyaKhalafi:feat/pydantic-queryset-item-names (4ad64c4) with develop (ef637d4)}