Sample upgrade

[skibitsky]

This PR introduces several improvements to the sample app as well as the CI workflow.

Sample App

• New scene loading flow for flexibility and (later) feature tags
• Settings view which currently shows client id and the app version
• Mixpanel to collect logs
• In-game debug console on native platforms
• Update default sample dapp ui to be more flexible and use UI Toolkit

CI/CD

• Builds Windows64, Android (IL2CPP), and WebGL on Ubuntu runners on every push
• WebGL is deployed on Vercel, with the preview link available in the comments. Other builds can be downloaded from the artifacts
• Disabled macOS builds because they require signing on macOS runner
• Use GitHub secrets for Mixpanel and Sentry tokens. These tokens can be shared publicly, but I excluded them from the source code so that we don't get events from modified copies of the sample app

[github-actions]

Deploy preview for w3m-unity ready!

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https://w3m-unity-dsk7ad42m-walletconnect1.vercel.app

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