Add util helpers

Add helper functions to easily pick deeply nested values returned by contract messages.

• pickDecoded
• pickError
• pickResultOk
• pickResultErr

See useink/utils documentation for details.

---

Helper functions that will reduce if statements and React code by up to 15%.

Example

// Let's pretend this returns a Result<{ Ok?: { flipped: true }, Err?: { Womp: string }> on each new block
const get = useCallSubscription(flipper, 'get') 

// Some of the new pick* functions
const okValue = pickResultOk(get.result); // This is { flipped: true } or undefined
const errValue = pickResultErr(get.result); // This is { Err: { Womp: string } or undefined

// INSTEAD OF DOING the deeply nested Choo Choo train from hell 🚊🔥
get?.result?.ok ? get.result.value.decoded?.Ok : undefined
get?.result?.ok ? undefined : get.result.value.decoded?.Err