Fixes # .

Summary/Motivation:

This PR resolves a couple small issues that snuck in over the last couple PRs:

• Moving the linux/conda build to Python 3.13 resulted in no coverage of pymumps (pymumps is only available on linux/osx through Python 3.12)
• Some Sphinx errors have snuck into the DoE API docs
• The new KNITRO interface raises "empty" DeveloperError exceptions that led to weird looking exceptions. This PR cleans up the rendering of "empty" DeveloperErrors (and adds tests to verify behavior)

Changes proposed in this PR:

• move linux/conda to Python 3.12
• resolve Sphinx errors in DoE
• improve DeveloperError string formatting
  • add some testing

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