Support pickling of a number of important structures to Python

[ChristopherRabotin]

Effects

One can now pickle the following data:

• TrkConfig
• FltResid
• GaussMarkov
• GroundStation
• Spacecraft
• SRPConfig
• DragConfig
  The following structures can now be loaded from YAML read by Python but not exported:
• OrbitEstimate
• SpacecraftDynamics

Moreover, the == in Python is now correctly supported wherever it was incorrect set up.

• More testing is needed before merging this

If this is a new feature or a bug fix ...

• Yes, the branch I'm proposing to merge is called issue-xyz where xyz is the number of the issue.

If this change adds or modifies a validation case

• No.

[ChristopherRabotin]

Self review approved, still needs more testing

[github-actions]

Visit the preview URL for this PR (updated for commit 91c2f35):

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