Backport mont_config_helper from 0.5.x to 0.4.x

[richardpringle]

Description

Closes #980
0.4.2 causes some compiler warnings with the MontConfig derivation. It would be great to get a patch release out with these changes from 0.5.x

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Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (master)
  Seems like there's no 0.4.x branch... think you could make one?
• Linked to GitHub issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• Wrote unit tests
  Just a scoping change on derived trait code
• Updated relevant documentation in the code
  same as above
• Added a relevant changelog entry to the Pending section in CHANGELOG.md
  I can do this if you'd like.
• Re-reviewed Files changed in the GitHub PR explorer

[richardpringle]

For scope warning reproduction instructions, see here

[richardpringle]

Hey @z-tech, I'm not going to spend time fixing the other warnings and it looks like CI is using some old github actions that it can't find.

I'm guessing that means we'll want to close this?

[z-tech]

As you like. Thanks for giving it a go.