Add Classy versions of Era witness functions

[smelc]

Changelog

- description: |
    Add `IsAllegraBasedEra`, `IsAlonzoBasedEra`, `IsBabbageBasedEra`, `IsConwayBasedEra`, `IsMaryBasedEra` type classes.
    Add `ToAlonzoScript` and `HasScriptLanguageInEra` type classes.
# 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

• Signed version of Add Classy versions of Era witness functions #537
• Also not on a clone, but on the true one cardano-api repo ©️