MAINT Remove redundant pytest asyncio markers

[Roman Lutz (romanlutz)]

Description

PyRIT uses asyncio_mode = "auto", so explicit @pytest.mark.asyncio decorators on async tests are redundant and prohibited by the test instructions. Remove all 33 remaining parameterless function-level decorators across the affected unit and integration tests while preserving skip, fixture, and parametrization decorators.

No parameterized, module-level, class-level, or loop-scope asyncio markers required exceptions.

Tests and Documentation

• Affected test collection passed.
• Combined affected test selection: 226 passed, 38 skipped.
• Ruff check and format checks passed for all changed files.
• File-scoped pre-commit hooks and git diff --check passed.
• Documentation and JupyText: N/A.