Emitted TXs: add NetworkID too

[WietseWind]

If you look at an emitted TX:
random example:
https://xahauexplorer.com/explorer/6D7A29E3021A3B2425ADC5AF5221D94E7D704DCBD59535D9EEE86A646D3D6D43

... it doesn't contain NetworkID. It obviously doesn't have to but if tools are relying on transactions to have NetworkID to decide how to deal with them when parsing, it would be useful to include it in emitted TXs too.

Workaroudn for now is to decide the CTID and get the NetworkID from there.

Alternatively!!

... Serialised tx lacks network ID field: maybe just rely on CTID anyway and decide to ignore this issue :)

[shortthefomo]

WIP https://github.com/lathanbritz/xahaud/tree/issue/259

[RichardAH]

WIP https://github.com/lathanbritz/xahaud/tree/issue/259

Interesting approach but I think it would be better to inject it directly into the actual serialized txn, otherwise you end up with serder issues (the serialized version differs from the deserialized version)