try: make Poseidon tree of all events in Block

[benjaminbollen]

this might still be too big a task for a single issue; so we can break down progress and follow up here

starting point:

• [x] assert sane leaf format to identify event; first suggestion (txIndex, address, eventTopic[], eventDataBlob)
• [x] how should these bytes be encoded for efficient use in proofs
• [x] attempt at making the merkle tree

[benjaminbollen]

we encode the event data in a p-adic representation (p = 2^64 - 2^32 + 1; Goldilocksfield)

maybe this can be done better with field extensions, but for now this was "straightforward"