fix: node fetch timeout

[vachmara]

Fix #712

This pull request updates how the undici HTTP client library is managed and integrated in the project, moving it from a direct dependency to a peer dependency, and adds improved Node.js HTTP timeout handling using undici's Agent. It also introduces corresponding test coverage for this new behavior.

Dependency management:

• Put undici and undici-types to peerDependencies in package.json, and marked them as optional in peerDependenciesMeta. This makes them optional peer dependencies instead of always-installed direct dependencies.

Node.js HTTP request improvements:

• In src/_api_client.ts, updated the request logic to dynamically import undici and set a custom Agent with timeout options for Node.js environments, improving HTTP timeout handling.

Testing:

• Added a new unit test in test/unit/api_client_test.ts to verify that the dispatcher with timeouts is set on HTTP requests in Node.js, and imported the required Agent and types from undici for testing.

Shout out to @yulisunny for spotting the issue, I tested this on vercel it's working!

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