feat: Add helper functions for claiming and attesting (#154)

* feat: Add attest and claimAttest

* Update polkadot

* Docs

* Remove skipped tests

* Fix test due to polkadot/api

* docs changes

* yarn doc

* Add utilities for claiming and attesting

* Docs

* add claim example

* Update SAFT hash

* Typo

* Fix tests

* add encodeunsigned (#155)

* export encodeUnsignedTransaction

* docs

* Update src/util/encodeUnsignedTx.ts

Co-authored-by: Amaury Martiny <[email protected]>

* Update api

Co-authored-by: joepetrowski <[email protected]>
Co-authored-by: joe petrowski <[email protected]>