Support for passing a custom provider that is *not* a signer

[TheWisestOne]

Currently, if the client passes a Provider into the DelegateCash constructor, it is assumed that this provider can also be used as a signer.

Specifically, these lines in the DelegateCash construtor:

    if (provider) {
      this.provider = provider;
      this.signer = this.provider.getSigner();
    }

In my use-case, I have a custom provider (spefically, an Alchemy node provider), which I want to use because it is not subject to rate limiting etc., but it is not valid for use as a signer.

Therefore, for me, during the DelegateCash instantiation, this line throws:

      this.signer = this.provider.getSigner();

with an error like:

Error: API provider does not support signing (operation=\"getSigner\", code=UNSUPPORTED_OPERATION, version=providers/5.7.2)

I'm only instantiating this object to call getDelegationsByDelegate, which doesn't use this.signer. So I want some way for me to pass this custom provider without the library trying to turn it into a signer, as I won't be using any of the signer functionality.

[ryespresso]

Thanks for the explanation! Originally, the only allowed type JsonRpcProvider or a Web3Provider. These work with Alchemy, etc but can see how it would be beneficial to allow any type so I made that adjustment in 0.4.5 to allow for providers with no signer.