Switch to new iris >= 3.10.0 API

[schlunma]

Description

Iris introduces a couple new features and also some breaking changes in v3.10.0:

• iris.experimental.ugrid is deprecated in favor for iris.mesh
• Mesh is now called MeshXY
• Keyword arguments for MeshXY.coord() have changed
• broadcast_to_shape now supports chunk argument (we can remove our custom solution)
• area_weights calculation is now lazy (we can remove our custom solution)

I opted for pinning iris instead of making it backwards-compatible so we can use all new features, which allows us to remove lots of lines in our code.

Addresses https://github.com/ESMValGroup/ESMValCore/issues/2492

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.70%. Comparing base (f969e82) to head (3a7a180). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2500 +/- ## ======================================= Coverage 94.69% 94.70% ======================================= Files 248 248 Lines 14071 14001 -70 ======================================= - Hits 13324 13259 -65 + Misses 747 742 -5 ```

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[valeriupredoi]

excellent, many thanks for taking on this one, Manu! Lemme know when you need a review :beer:

[schlunma]

Since iris released v.3.10.0 today, this is ready for review now!

[valeriupredoi]

will do a more reviewey review tomorrow, in the meantime, be advised of this for future rc_iris stuffs https://github.com/conda-forge/iris-feedstock/issues/115

[schlunma]

@bouweandela please merge if you're happy with this 👍

[schlunma]

Thanks V for reviewing 🍻