fix warning and flake

[zzstoatzz]

see warnings and failures https://github.com/jlowin/fastmcp/actions/runs/12131427611

• fix pytest warnings "cannot collect" TestClassNotGroupingCases -> SomeClassNotGroupingCases
• order-independent check for test_dev_with_dependencies
• adds pytest-flakefinder as a dev dep so I can do

» pytest tests/test_cli.py -k with_dep --flake-finder

tests/test_cli.py ....................................................................................................    [100%]

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