feat: support dynamic outputs

[mduthey]

While implementing an airdrop in tx3, I hit a limitation.

The sender holds N tokens, and the transaction must distribute them to Y recipients.
This requires a dynamic number of outputs based on input data, but outputs appear to be static.

I also tried modeling recipients/allocations using List<...>, but I could not make it work for generating outputs (seems unsupported for this use case).

In addition, some airdrops require sending more than one token to the same address, and I did not find a clear way to represent multiple token allocations per recipient in the transaction definition.

For example:
I need to distribute 6 TOKEN to 3 addresses:

Address 1 → 2 TOKEN
Address 2 → 1 TOKEN
Address 3 → 3 TOKEN
In this case, the transaction must create 3 outputs dynamically based on the recipient list and amounts.