Investigate mapValues type mapping issue

[nflaig]

Current implementation or rather the typing / generics of mapValues function to seem to be incorrect, requiring to type cast the returned value (although the implementation itself works as expected)

lodestar/packages/api/src/utils/client/client.ts

Line 124 in c635098

}) as unknown as ApiWithExtraOpts<Api>;

This is the current implementation which needs to be reviewed / reworked

lodestar/packages/utils/src/objects.ts

Lines 67 to 76 in 8b6ecc4

	export function mapValues<T extends {[K: string]: any}, R>(
	obj: T,
	iteratee: (value: T[keyof T], key: keyof T) => R
	): {[K in keyof T]: R} {
	const output = {} as {[K in keyof T]: R};
	for (const [key, value] of Object.entries(obj)) {
	output[key as keyof T] = iteratee(value, key);
	}
	return output;
	}

See previous discussion for more context #6749 (comment)