fix(cloudflare): Instrument custom WorkerEntrypoint RPC methods

[akshitsinha]

withSentry() only wraps the lifecycle handlers on WorkerEntrypoint (fetch, scheduled, queue, tail). Custom RPC methods never get wrapped, so errors thrown in them are not captured and trace propagation does not work for them.

This mirrors what we already do for Durable Objects in durableobject.ts: the constructor proxy returns an instance proxy that catches RPC methods as workerd accesses them, and wraps them using the same wrapMethodWithSentry helper.

The generic typing change on instrumentWorkerEntrypoint / WorkerEntrypointConstructor also fixes #22233, where the Env generic was ignored and the constructor parameter was always typed as the global cloudflareEnv.

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Also fixes #22233

[JPeer264]

Thanks a lot for the PR. It actually looks pretty good already - I just have couple of comments, nothing critical.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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