Introduce EasyEvidence type class

[Jimbo4350]

Changelog

- description: |
    Introduce MainnetValue type class
# uncomment types applicable to the change:
  type:
   - feature        # introduces a new feature
  # - breaking       # the API has changed in a breaking way
  # - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - improvement    # QoL changes e.g. refactoring
  # - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

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Checklist

• Commit sequence broadly makes sense and commits have useful messages
• The change log section in the PR description has been filled in
• New tests are added if needed and existing tests are updated. These may include:
  • golden tests
  • property tests
  • round trip tests
  • integration tests
    See Running tests for more details
• The version bounds in .cabal files are updated
• CI passes. See note on CI. The following CI checks are required:
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  • Code builds on Linux, MacOS and Windows for ghc-8.10.7 and ghc-9.2.7
• Self-reviewed the diff

[newhoggy]

I think this could be problematic. If we code against a specific era like this, it could break on a hard fork.

For example if you're running a service and your code is using this function that says mainnet is babbage and then the hardfork takes mainnet to conway, your service stops working.

This is especially important since we no longer era cast transactions and other values.

[Jimbo4350]

forEraMaybeEon already has the functionality I was looking for