Add middleware helpers for Mina

[SpaceManiac]

Draft pending #389.

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• Improve exported API of mina-delegation package to deal with usability issues.
  • Rename DelegationOrder to DelegationCommand.
• Add MinaDelegationCache to @paima-sdk/providers.
  • Given a gameName, this uses localStorage + a background worker to generate and cache a DelegationCommand proof.
  • Necessitated some build system fixups.
• Let some IProvider.signMessage implementations accept Uint8Array in addition to string.
  • Mina itself is excluded because Auro Wallet's API accepts strings only.
  • Therefore the IProvider interface itself only accepts string still.
  • It's still not advised to pass non-UTF-8 data, e.g. EVM personal_sign data is treated as text, so it won't look pretty.
  • Mainly included because of code improvements to how the strings get hex'd.

TODO:

• (?) Rename mina-delgation back to mina-contracts since caching is out & no longer demands that we split packages per program/contract.

Demo at PaimaStudios/paima-game-templates#81.