Improve QuerySet integer indexing error guidance

[samdolan]

Description

This PR improves the error guidance for invalid integer indexing on the lazy QuerySet.

• Adds a dedicated ParamsError branch in QuerySet.__getitem__ for integer keys.
• Updates the error message to explain lazy evaluation and actionable alternatives:
  await queryset.first(), await queryset.offset(n).first(), or await queryset.all() and index the returned list.
• Adds test_integer_indexing_not_supported in tests/test_queryset.py to cover this behavior.

No functional change to valid slicing (queryset[start:stop]).

Motivation and Context

QuerySet supports slicing but not list-style integer indexing.
Before this change, users got a generic error that didn’t explain the async/lazy usage pattern clearly.
This update makes the failure mode easier to understand and recover from.

How Has This Been Tested?

• uv run --frozen --group test --group contrib --extra psycopg pytest -q tests/test_queryset.py
  • Result: 64 passed, 8 skipped
• uv run --frozen --group dev ruff check tests/test_queryset.py tortoise/queryset.py
  • Result: All checks passed

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.

[samdolan]

This came up in an interview and the output confused us both a bit. Thought I would pay it forward and have a more discrete error message there.

[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

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

[abondar]

Please fix lint

[coveralls]

Pull Request Test Coverage Report for Build 21883272953

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