Add configuration options to duration extension

[user27182]

Purpose

The duration extension is great but is not configurable. It currently only shows 5 slowest durations and only
prints to the console.

This PR adds configuration options:

1. duration_n_slowest to print any number of durations to console (not just 5)
2. duration_print_slowest to enable/disable printing to console altogether
3. duration_write_json to write all durations to a JSON file
4. duration_print_total to print the total read time to console
5. duration_limit to emit a warning for long durations above the limit

No tests are yet included. I am a first time contributor and not familiar with dev tools and conventions here... I may need some extra help.

[user27182]

This is ready but I don't think I have the tests configured properly. When I run each test individually locally they each pass on their own. But running the whole suite causes some to fail. Is there some kind of interaction between tests?

[AA-Turner]

Please add yourself to AUTHORS too. I think it's better to add each option as a new top-level option rather than as a dictionary.

[user27182]

I'm going to modify the API a bit to better match pytest. pytest uses --durations=0 to show all durations, whereas this extention currently uses n_slowest=-1 to do the same, so will rename n_slowest to durations and change -1 to 0.
Will rework the console formatting too to match pytest.

[user27182]

I've also added a new option to limit the duration to some value. Should be ready now.

CI is green except there are seemingly unrelated autodoc Python 3.14 errors...