Use Error.tag/tag_arg instead of stringifying errors

[mrmr1993]

This PR replaces some Error.to_string_hum with Error.tag and Error.tag_arg. These add additional data to errors without forcing their format, and play much more nicely with our pretty-printing in the logger.

A few uses still remain, mostly where the error is passed through calls between being cast to a string and being re-cast to an error. These are few and can be done as follow-up work at some later time.

Checklist:

• Document code purpose, how to use it
  • Mention expected invariants, implicit constraints
• Tests were added for the new behavior
  • Document test purpose, significance of failures
  • Test names should reflect their purpose
• All tests pass (CI will check this if you didn't)
• Serialized types are in stable-versioned modules
• Does this close issues? List them:

Closes #6699

[psteckler]

Sanity reigns!