Handy attribute/numpy-like statistics and mark real (S3, https) tests to slow

[valeriupredoi]

Description

Contributes towards #231

A more convenient way to handle stats:

File

    active = Active(ncfile, "cl")
    result2 = active.mean[4:5, 1:2]

Dataset

    ds = pyfive.File(uri)[ncvar]
    av = Active(ds)
    av_slice_min = av.mean[3:5]

Note the components attr is all under the hood now.

The components attr is back again at the user's discretion, thanks to @davidhassell pointing out that's actually needed to be variable.

Also, I made the real S3 and https tests slow, and the GHA is now skipping them only for a PR (it runs them when we merge, and nightly). It's incredible how much variability there is in terms of running a set of such simple tests, with times ranging from a couple minutes to even 20-30min; network load is bloody big!

Skipping the https tests via slow decreases our measured coverage by 6% (from almost 92% to 86%), but that's fine, we actually run them, codecov measures coverage off the tests run in the PR.

Before you get started

• ☝ Create an issue to discuss what you are going to do

Checklist

• This pull request has a descriptive title and labels
• This pull request has a minimal description (most was discussed in the issue, but a two-liner description is still desirable)
• Unit tests have been added (if codecov test fails)
• Any changed dependencies have been added or removed correctly (if need be)
• All tests pass

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.07%. Comparing base (aa746b4) to head (683fb7c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #253      +/-   ##
==========================================
- Coverage   91.18%   85.07%   -6.11%     
==========================================
  Files           7        7              
  Lines         635      650      +15     
==========================================
- Hits          579      553      -26     
- Misses         56       97      +41     

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[valeriupredoi]

@davidhassell cheers for the (verbal) review, I think I've plopped all in here for an actual review, please 🍻

[davidhassell]

All good!

[valeriupredoi]

great many thanks @davidhassell 🍺