getSigner is not exposed on MulticallProvider

[grepfruit19]

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In my app, using the ethers.WalletProvider, I often call provider.getSigner(), but wrapping the WalletProvider with the MulticallProvider does not expose this method, so I have to fetch the nested WalletProvider in order to access that. I think the MulticallProvider should expose that method natively.

[grepfruit19]

I wonder if this is as simple as adding getSigner to the list of ProxyMethods here? If it is I'm happy to create a PR for this, just looking for some guidance:

https://github.com/0xsequence/sequence.js/blob/master/packages/multicall/src/providers/provider.ts#L8