Optimize transaction generators

In their downstream uses in `ouroboros-consensus`, we've found the Shelley transaction generators are slow. From this excerpt from the `.prof` summary, it looks like they're allocating a lot and hence are slow.

```
COST CENTRE MODULE SRC %time %alloc

choose Test.QuickCheck.Gen Test/QuickCheck/Gen.hs:130:1-59 28.3 36.6
genTx Test.Shelley.Spec.Ledger.Generator.Utxo src/Test/Shelley/Spec/Ledger/Generator/Utxo.hs:(170,1)-(237,86) 4.5 4.2
shuffle Test.QuickCheck.Gen Test/QuickCheck/Gen.hs:(217,1)-(219,55) 3.9 6.9
```

By accident, we didn't retain enough info to identify the specific problematic calls, but the `genTx` is at least incriminated. Here's the excerpt from the `.prof` body:

```
COST CENTRE MODULE SRC no. entries %time %alloc %time %alloc

genTx Test.Shelley.Spec.Ledger.Generator.Utxo src/Test/Shelley/Spec/Ledger/Generator/Utxo.hs:(170,1)-(237,86) 111572 19825 4.5 4.2 47.2 66.1
shuffle Test.QuickCheck.Gen Test/QuickCheck/Gen.hs:(217,1)-(219,55) 111593 133890 3.9 6.9 36.7 56.8
choose Test.QuickCheck.Gen Test/QuickCheck/Gen.hs:130:1-59 111599 0 28.1 36.4 30.2 42.2
```

So it's the `shuffle`s in `genTx`. They're allocating "too much".

At a glance, I think multiple of the uses of `shuffle` could be manually fused. For example:

https://github.com/input-output-hk/cardano-ledger-specs/blob/befbf160ed840d2d6ad843902c9f668507dc7838/shelley/chain-and-ledger/shelley-spec-ledger-test/src/Test/Shelley/Spec/Ledger/Generator/Utxo.hs#L559-L560

In this one, the `utxo` list is probably quite large. And then we immediately project out just a few (I _think_ `maxNumGenInputs` is just `10` here.). So just generating 10 indices without replacement and then projecting those would avoid massive allocation (I think).

Hopefully there are similarly straight-forward opportunities for the other `shuffle` uses and whatever else follow-up profiling identifies.