Added dataless rolling window, _intersect and interpolate

[ESadek-MO]

• rolling_window
• intersection

Interpolation and regridding are both quite involved. For completion sake, I would've liked to get interpolation in, but I don't think it's worth the time it would take to get it right. Some of the underlying logic just doesn't work with dataless cubes, and would need chasing around the place.

So for now, I think this is it for single operations. If there's a call in the future for interpolate or regridding (the latter seems particularly unlikely), then we can work towards them then.

[codecov]

Codecov Report

❌ Patch coverage is 89.28571% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.31%. Comparing base (9c06cca) to head (80597ff).

Files with missing lines	Patch %	Lines
lib/iris/cube.py	89.28%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6757      +/-   ##
==========================================
+ Coverage   90.29%   90.31%   +0.01%     
==========================================
  Files          91       91              
  Lines       24656    24665       +9     
  Branches     4618     4620       +2     
==========================================
+ Hits        22264    22277      +13     
+ Misses       1620     1618       -2     
+ Partials      772      770       -2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.