[fix] update to ghc 94

[MangoIV]

• fix the compile errors
• fix the test failures
• add github workflows to verify it keeps working
• add nix env
• prepare flake update such that we can update easily in the future
• reformat with stylish-haskell as good as possible

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PR Submission Checklist for internal contributors

• The PR Title

  • conforms to the style of semantic commits messages¹ supported in Wire's Github Workflow²
  • contains a reference JIRA issue number like SQPIT-764
  • answers the question: If merged, this PR will: ... ³

• The PR Description

  • is free of optional paragraphs and you have filled the relevant parts to the best of your ability

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What's new in this PR?

Issues

• update to ghc >= 9.4

Causes (Optional)

• update wire-server beyond ghc 9.2

Solutions

• add some CPP to cover the ghc api changes

Dependencies (Optional)

n/a

Needs releases with:

• GitHub link to other pull request

Testing

Test Coverage (Optional)

• I have added automated test to this contribution

How to Test

• add a workflow that tests both supported ghc versions

Notes (Optional)

n/a

Attachments (Optional)

n/a

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PR Post Submission Checklist for internal contributors (Optional)

• Wire's Github Workflow has automatically linked the PR to a JIRA issue

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PR Post Merge Checklist for internal contributors

• If any soft of configuration variable was introduced by this PR, it has been added to the relevant documents and the CI jobs have been updated.

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References

1. https://sparkbox.com/foundry/semantic_commit_messages
2. https://github.com/wireapp/.github#usage
3. E.g. feat(conversation-list): Sort conversations by most emojis in the title #SQPIT-764.