Genesis nonce scheme

[lrettig]

Under account unification, each principal account is free to implement its own nonce scheme. For genesis, we need to design and implement one standard, recommended nonce scheme that will be included in the genesis smart contracts.

See https://community.spacemesh.io/t/nonce-schemes-and-account-unification/202

Other links to read:

• https://ethresear.ch/t/account-abstraction-radically-simplified/3769/17
• https://ethresear.ch/t/using-binary-vector-clocks-to-replace-transaction-nonces/7290/1

SMIP: https://github.com/spacemeshos/SMIPS/issues/79

Related: #20

• [x] Review forum thread
• [x] Update tx structure doc
• [x] Review tx structure doc with @noamnelke and @dshulyak
• [x] Decide how/where tx sorting happens (outside VM, as cmax | ~noncemask)
• [x] Decide how/where nonce checking (validity predicate) happens (inside verify())
• [x] Decide how/where nonce update happens (inside VM, NonceUpdate template method)
• [x] Dev task breakdown (#104)

[lrettig]

Noam described this in tx structure doc

[lrettig]

Finished reviewing forum thread, and updated tx structure doc. Next step: discuss with Noam and Dima, make final decisions (see checklist above), then write dev task breakdown.

[lrettig]

Discussed this with @noamnelke and @selfdual-brain today. We decided to stick with a simple "int nonces with gaps" scheme: see #150 for the straightforward proposed design and dev tasks breakdown. We'll continue to discuss more sophisticated, generalized nonce schemes for the future.