fix(types): assignability error in tests stub

[dimitropoulos]

I happened to notice there's a few errors in index.test.ts. Seems like that's because the build skips the tests (naturally) and vitest doesn't do typechecking.

here's the error:

Argument of type '(i: number) => Promise<number>' is not assignable to parameter of type 'Unstubify<((i: Unstubify<number>) => Promise<number> & { toString: (radix?: Unstubify<number | undefined>) => Promise<string> & { [x: number]: Promise<...> & ... 2 more ... & StubBase<...>; ... 50 more ...; toWellFormed: () => Promise<...> & ... 2 more ... & StubBase<...>; } & { ...; } & StubBase<...>; ... 4 more .....'.
  Type '(i: number) => Promise<number>' is not assignable to type '(i: number) => number'.
    Type 'Promise<number>' is not assignable to type 'number'.ts(2345)

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[Copilot]

Pull request overview

This PR fixes a TypeScript type assignability error in the test suite and corrects a spelling mistake. The build process skips tests and vitest doesn't perform typechecking by default, which allowed these issues to go undetected.

• Updated the type signature of callFunction to correctly accept async functions returning Promise<number> instead of synchronous functions
• Corrected spelling typo in test description

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
__tests__/test-util.ts	Fixed type signature of callFunction method to accept RpcStub<(i: number) => Promise<number>> instead of RpcStub<(i: number) => number>, resolving TypeScript assignability error
__tests__/index.test.ts	Corrected spelling of "functinos" to "functions" in test case description

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[dimitropoulos]

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commit: f15b1f3

[kentonv]

Thanks!

FWIW, I think there are also a couple places in the test where TypeScript complains about infinite recursion, which seems like a deeper problem with the way the types work right now that needs to be addressed.

types.d.ts actually originates as a copy of workerd's rpc.d.ts, but with several refinements (that should probably be backported to workerd at some point). However, it is still a bit janky. Could definitely use some help from a TypeScript expert to get this all working properly!