Add 'Convert Experimental.Era MaryEraOnwards' instance

[smelc]

Changelog

- description: |
    Add 'Convert Experimental.Era MaryEraOnwards' instance
# 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
  # - refactoring    # QoL changes
  # - 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

Add instance required by CLI (see IntersectMBO/cardano-cli#988)

How to trust this PR

It's only an instance addition, and a legit one.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• Self-reviewed the diff

[Jimbo4350]

This is indicative of a deeper cardano-api issue. We should not be converting to the "old api".

[smelc]

I agree, but this is required until we fully separate the old and new apis right?

And we already do that anyway (on master at the time I'm writing this):

cardano-api/cardano-api/internal/Cardano/Api/Experimental/Eras.hs

Line 194 in 76fba1c

instance Convert Era Api.CardanoEra where

[smelc]

@Jimbo4350> The issue is as follows right now:

Here (within the implementation of transaction build-estimate): https://github.com/IntersectMBO/cardano-cli/blob/3c0af7a8088b7c885ddc3c5c03734f2a2d5577cb/cardano-cli/src/Cardano/CLI/EraBased/Run/Transaction.hs#L509

We call API's estimateBalancedTxBody:

cardano-api/cardano-api/internal/Cardano/Api/Fees.hs

Line 191 in 76fba1c

estimateBalancedTxBody

And the thing is that transaction build-estimate takes an experimental witness, whereas estimateBalancedTxBody expects a MaryEraOnwards witness.

So I'm not sure how you want to fix that?