WIP: Preliminary ghc 9.14 support

[erikd]

• Currently using ghc-9.14.0.20250908.
• This GHC has a bug that needs to be fixed before the real 9.14 release.
• This bug required the adding of a large number of CPP guarded -Wno-redundant-constraints which need to be removed.
• Huge number of allow-newers, the majority of which need to be removed.

Pre-submit checklist:

• Branch
  • Tests are provided (if possible)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
  • Changelog fragments have been written (if appropriate)
  • Relevant tickets are mentioned in commit messages
  • Formatting, PNG optimization, etc. are updated
• PR
  • (For external contributions) Corresponding issue exists and is linked in the description
  • Targeting master unless this is a cherry-pick backport
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested

[github-actions]

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