Add points/bounds formatting method and class, handling datetimes

[stephenworsley]

Addresses #4508.

To access a numpy array of formatted strings for a coordinates points, for example, this can be called as follows:

coord.as_string_arrays().points

Note that calling the points in this way avoids having to calculate the bounds and vice versa.

---

To print a formatted summary of both the points and bounds:

print(coord.as_string_arrays())

To format dates in a particular form, e.g:

fmt = "%Y-%m-%d"
print(coord.as_string_arrays(fmt))

Note that this can also format other data types like foat or int.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.12%. Comparing base (043b0bc) to head (895483d).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6978      +/-   ##
==========================================
+ Coverage   90.11%   90.12%   +0.01%     
==========================================
  Files          91       91              
  Lines       24912    24951      +39     
  Branches     4675     4683       +8     
==========================================
+ Hits        22449    22488      +39     
  Misses       1684     1684              
  Partials      779      779              

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[ESadek-MO]

A couple of doc changes only! One of which is a whatsnew!

[scitools-ci]

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[ESadek-MO]

Couple more!

This change is unique to Iris, and more specifically this particular whatsnew

[ESadek-MO]

Thanks @stephenworsley !

[ESadek-MO]

I meant to approve...