Add Ruff rule: useless-expression (B018)

[genedan]

What this rule does is flag statements that have no effect, for example:

def my_function(x: int) -> int:
    1 + 1
    return x + 5

1 + 1 would have no effect, and Ruff should flag it so that it can be removed.

[Abhayindia]

@genedan happy to take this. Enabling B018 flags 10 spots right now: one is a genuine missing () in munich.py, and the rest are a mix of stray leftover lines and deliberate bare expressions inside notebook cells and pytest.raises blocks. Do you want notebooks kept in scope (with the intentional test lines getting a noqa), or should I exclude the notebooks and just clean the library + test code?

[genedan]

I think Ruff has already been configured to check notebooks, with the exception of the sandbox tutorial one.

For this issue, you'd just need to add the rule and update the files that are "grandfathered" into the review process (listed in [tool.ruff.lint.per-file-ignores])..

[genedan]

@Abhayindia, you may notice that I'm adding multiple issues for several rules - it's OK if you want to handle several of them in a single PR.