Add format agent copy and equality methods

[jrackham-mo]

🚀 Pull Request

Description

Closes #6108. Adds a copy method to FormatAgent, which creates a new FormatAgent from the format specs. Also adds an equality method which compares the format specs.

The use case for this is to temporarily modify the FORMAT_AGENT in a custom load, and then restore it so that we don't change standard iris.load behaviour outside of the custom load.

[CLAassistant]

All committers have signed the CLA.

[codecov[bot]]

Codecov Report

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

Project coverage is 89.82%. Comparing base (b8f554f) to head (0b08f0c). Report is 78 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6119      +/-   ##
==========================================
+ Coverage   89.77%   89.82%   +0.04%     
==========================================
  Files          88       88              
  Lines       23026    23150     +124     
  Branches     5036     5043       +7     
==========================================
+ Hits        20672    20794     +122     
- Misses       1623     1624       +1     
- Partials      731      732       +1     

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