Update `ethers` dependencies

[ndzik]

The SDK seems to be using outdated ethers dependencies. This makes it awkward to use in external projects because depending on whether one uses yarn or npm to resolve project dependencies one receives the error:

Argument of type 'JsonRpcSigner' is not assignable to parameter of type 'Signer'.
The types returned by 'provider.addListener(...).resolveName(...)' are incompatible between these types. 
Type 'Promise<string | null>' is not assignable to type 'Promise<string>'. 
Type 'string | null' is not assignable to type 'string'. Type 'null' is not assignable to type 'string'.

This should be solvable by updating ethers together with the contract bindings, which is related to typechain.

[RmbRT]

On hold until hardhat compile supports ethers v6

[DragonDev1906]

Together with #152