Rename era to sbe when type is ShelleyBasedEra

[newhoggy]

Changelog

- description: |
    Rename `era` to `sbe` when type is `ShelleyBasedEra`
  compatibility: no-api-changes
  type: maintenance

Context

It can be confusing when era has the type ShelleyBasedEra era because it is also used for values of the type CardanoEra era.

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
  • roundtrip tests
• The version bounds in .cabal files are updated
• CI passes. See note on CI. The following CI checks are required:
  • Code is linted with hlint. See .github/workflows/check-hlint.yml to get the hlint version
  • Code is formatted with stylish-haskell. See .github/workflows/stylish-haskell.yml to get the stylish-haskell version
  • Code builds on Linux, MacOS and Windows for ghc-8.10.7 and ghc-9.2.7
• The changelog section in the PR is updated to describe the change
• Self-reviewed the diff

Note on CI

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