SiweExternal Auth - Login through static React EOA

[0xFirekeeper]

Allows you to login to otherwise native-unavailable wallets such as Abstract Wallet & Coinbase Smart Wallet through a flow similar to OAuth, using SIWE.

Closes TOOL-3134
Related TOOL-3137

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PR-Codex overview

This PR introduces support for a new authentication method called SiweExternal in the InAppWallet system. It enhances the wallet's capabilities to integrate with external sign-in processes, improving user authentication options.

Detailed summary

• Added SiweExternal to AuthProvider enumeration.
• Implemented SignInWithSiweRawAsync method in EmbeddedWallet.
• Created PreAuth_SiweExternal and LoginWithSiweExternal methods in EcosystemWallet.
• Updated IThirdwebWallet interface to expose properties and methods publicly.
• Added ToString method in LoginPayloadData for JSON serialization.

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[linear]

TOOL-3134 AuthProvider.SiweExternal static flow

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 76.71%. Comparing base (0c94da4) to head (af9f663).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
Thirdweb/Thirdweb.Wallets/IThirdwebWallet.cs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #123      +/-   ##
==========================================
+ Coverage   76.68%   76.71%   +0.03%     
==========================================
  Files          28       28              
  Lines        4799     4802       +3     
  Branches      665      665              
==========================================
+ Hits         3680     3684       +4     
- Misses        945      946       +1     
+ Partials      174      172       -2     

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