Merge #3725

3725: Re-write withRecentEra to require less nesting r=Anviking a=Anviking

It seems we can replace

```haskell
main = do
    era <- getEra
    withRecentEra era $ \(recentEra :: WriteTx.RecentEra era) -> do
        doStuff recentEra
```
with
```haskell
main = do
    era <- getEra
    AnyRecentEra (recentEra :: WriteTx.RecentEra era) <- guardIsRecentEra era
    doStuff recentEra
```
to save on precious horizontal space!

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Co-authored-by: Johannes Lund <johannes.lund@iohk.io>