feat: use worker.mts for pure ESM

[JounQin]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)

Problem

A lot of await import in https://github.com/mdx-js/eslint-mdx/blob/3bdd2eb88244aeda636c11f3ccaff35ae2c05ac2/packages/eslint-mdx/src/worker.ts and the hack loadEsmModule

eslint-mdx/packages/eslint-mdx/src/helpers.ts

Lines 60 to 64 in 3bdd2eb

	export const loadEsmModule = <T>(modulePath: URL | string): Promise<T> =>
	// eslint-disable-next-line @typescript-eslint/no-implied-eval, no-new-func
	new Function('modulePath', `return import(modulePath);`)(
	modulePath,
	) as Promise<T>

is unnecessary.

Solution

Just change worker.ts to pure ESM worker.mts which is just supported by synckit natively.

Alternatives

N/A