[WIP] v3 blocks and transactions (no redundant input features)

[antiochp]

[WIP]

• v2 inputs are FeaturesAndCommit
• v3 inputs are CommitOnly

There is some complexity here as translating a v3 input to v2 requires "external" data (the output features). The output features must be read from the output MMR which must be in the correct state itself, based on current block being processed.

Additionally this messes with sort order as we sort based on hash and the data being hashed is different.
So converting v2->v3 and v3->v2 cannot be done purely on individual inputs.
It must be handled at the collection level as the collection of inputs must be reordered to account for the new sort order.

Resolves #3378.

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TODO -

• Inputs enum variants CommitOnly, FeaturesAndCommit
• CommitWrapper for sorting commitments correctly by hash()
• serialization support for Input variants (v2 vs. v3)
• block support
  • receive v2
  • receive v3
  • broadcast/send v2
  • broadcast/send v3
  • convert v2 -> v3
  • convert v3 -> v2
  • store in db in v2 (for backward compatibility)
• transaction support
  • convert v2 -> v3
  • handle as v3 internally in txpool
  • convert to v2 for backward compatibility for v2 peers
  • relay/send v2
  • relay/send v3
• version negotiation (make sure this is working as expected)

[antiochp]

Replaced with smaller more focused refactor PRs (various) and #3419.