Feat: Add support for arbitrary # of multisig signers (#152)
* Last try with `auth_fields` as ArrayVec
* Passes unit tests with `auth_fields_raw` in `MultisigSpendingCondition`
* Add `_num_multisig_fields` to FFI
* Add support for m-of-n multisig in actions.h
* Fix `validate_post_sig_hash_chain()`, multisig integration tests pass now
* feat: Add support for new SIP (SIP-02x: Non-sequential multisig transactions)
* fix: Remove extra hash step for first signer in multisig tx
* fix: Update screenshots so all zemu tests pass
* chore(actions.h): Update comments
* chore: Clean up unused variables in multisig test
* test: Add test for order-independent multisig
* test: Add separate screenshots for order-independent multisig test
