Replace IsCardanoEra and IsShelleyBasedEra contraints in GADT constructors with Typeable

[newhoggy]

Changelog

- description: |
    Replace `IsCardanoEra` and `IsShelleyBasedEra` contraints in GADT constructors with `Typeable`
# 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...

Context

There are very few places where we need IsCardanoEra and IsShelleyBasedEra in these GADTs.

In these few remaining places, cardanoEraConstraints and shelleyBaseConstraints can be used to get the constraints instead.

Removing these constraints is helpful because whilst it makes it more convenient when unpacking the GADT, when constructing the GADT it is more inconvenient because the declared constraints need to be available on construction.

Moreover, the removal of these constraints makes the modified GADTs more compatible with EraInEon.

Downstream cardano-cli changes: IntersectMBO/cardano-cli#435

How to trust this PR

Highlight important bits of the PR that will make the review faster. If there are commands the reviewer can run to observe the new behavior, describe them.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff

[Jimbo4350]

What does this change look like in cardano-cli?

[newhoggy]

What does this change look like in cardano-cli?

There is a link in the PR description.

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