fix(datum): keep the original bytes of decoded inline datums

[solidsnakedev]

Decoding a transaction dropped each inline datum's original bytes, and encoding rebuilt them with the default data layout. When the layout differed, for example a definite map a10102 that became bf0102ff, re-encoding changed the body. Adding a witness with addVKeyWitnessesBytes then changed the transaction id, and the node rejected the transaction with 3100 (invalid signatures).

Decoding now records the exact bytes inside tag 24 against the InlineDatum it returns, and encoding writes them back when it is given that same object. A new or edited datum is a new object, so it still gets the default encoding. The record lives in a new shared OriginalBytes module, a WeakMap from a decoded object to its bytes, which later steps of #581 will reuse for other parts of the transaction.

Closes the inline-datum part of #576. Step 1 of #581.