refactor: Simplify inventory client parsing

[pxrl]

This helps to drop an UMA dependency, and is arguably nicer because it doesn't corce the js Object to and from a string type.

[pxrl]

replaceAddressCase() taken from here: https://github.com/UMAprotocol/protocol/blob/e9af17eb2985f482635b9009a1174a694a025d31/packages/common/src/FormattingUtils.ts#L155

In general I'm not a fan of the former implementation because it coerces an object into a string in order to achieve address normalisation into checksum case, so I opted to operate directly on the string here.

[nicholaspai]

Do you think we should make this a helper function? I think there are several other places where we expect an address string set in the .env that might not be checksummed

[pxrl]

We can make it a utility function; I only did it here because this was the only place I could see that we actually normalised addressed on input.

I'll update accordingly 👍

[james-a-morris]

It may be easier to use a reviver in this case. JSON.parse's second parameter is an optional function that looks at keys/values. We could probably create a reviver function like:

/**
 * Converts a potential string/array of strings that match an address into a checksummed address
 **/
export function checksumAddress(value: unknown): unknown {
    const isArray = Array.isArray(value);
    const result: unknown[] = (isArray ? value : [value]).map((v) => utils.isAddress(v) ? utils.getAddress(v) : v;
    return isArray ? result : result[0];
}

JSON.parse(
    RELAYER_INVENTORY_CONFIG ?? {},
    (, v) => checksumAddress(v)
)

[james-a-morris]

Left a comment to possibly add discussion about the readability of the parse function