[relay, auth-kit, auth-client] feat: support redirectUrl

[deodad]

Motivation

Allow mobile apps using the connect flow to instruct wallet clients to return the user back to the app after signing.

Change Summary

• support redirectUrl when initiating a sign in
• remove ethers as a hard dependency from auth-client
• add an expo example application

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[dalechyn]

hey, that's probably a bit too late to comment, but why ethers was added as a peer dep when public provider can be used from viem directly?

[deodad]

@dalechyn ethers is a dependency of the siwe package

[deodad]

@dalechyn I saw some of your other comments, thank you—responded to some but feel free to open a concise PR with the others