feat(brownie): add selector and equality fn support to useStore

[okwasniewski]

Summary

• Add optional selector and equalityFn params to useBrownieStore hook
• Use useSyncExternalStoreWithSelector for optimized re-renders
• Export shallow equality helper (zustand-style)
• Add tests for shallow comparison
• Update TesterIntegrated example with selector usage

New API:

// With selector - only re-renders when selected value changes
const [count, setState] = useStore('Store', s => s.count)

// With selector + shallow equality for objects
const [user, setState] = useStore('Store', s => s.user, shallow)