Improve QuerySet integer-indexing error guidance

[sam-dawnops]

Description

Add a dedicated ParamsError message for integer indexing on QuerySet and cover it with a regression test.

Motivation and Context

QuerySet is lazy and supports slicing, but queryset[5] currently raises a generic message. This change makes that failure mode clearer and tells users how to evaluate/query for a single item correctly.

How Has This Been Tested?

• uv run --frozen --group test --group contrib --extra psycopg pytest -q tests/test_queryset.py
• uv run --frozen --group dev ruff check tests/test_queryset.py tortoise/queryset.py

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-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

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_{Comparing sam-dawnops:fix/queryset-integer-index-guidance (01f2d83) with develop (fe73270)}

[coveralls]

Pull Request Test Coverage Report for Build 21883100900

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.005%) to 82.483%

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Files with Coverage Reduction	New Missed Lines	%
tortoise/queryset.py	1	96.07%

Totals
Change from base Build 21856593682:	0.005%
Covered Lines:	10422
Relevant Lines:	12169

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💛 - Coveralls