fix: pin privy dependency versions

[CarsonRoscoe]

Description

Privy, specifically @privyio/server-auth, had a bunch of recent back-to-back updates that changed the underlying dependencies of the package. In doing so, a number of changes were made recently that break installing AgentKit.

I attempted to find the last version of @privyio/server-auth (and a corresponding @privyio/public-api released the same day) that satisfies this issue. However, in doing so, I discovered that there have been interface-breaking Privy updates. We cannot trust the minor versions or even patch versions to not introducing breaking changes to either dependencies or interfaces.

Therefore, this PR simply goes back to the last guaranteed trusted version, and pins it by removing the ^ on the dependency.

We can fast-follow with a more robust solution, however this hotfix is needed to fix new installations of AgentKit.

Tests

Validate the issue by running npm run create onchain-agent@latest, and run through the setup with Langchain. Run npm install, try to chat with the bot, and you will see a series of dependency issues in the console, all stemming from privyio server.

Doing the same locally with this new version produces an agent example which works out of the box

[cb-heimdall]

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