Support directly setting storage attributes

[evshi]

Is your feature request related to a problem? Please describe.
Flutter allows you to change storage variables using assignment syntax e.g.

ensemble.storage.var = value

Describe the solution you'd like
React prescribes that state mutations must be functions. However this can potentially be worked around in jotai by creating a focus atom on that specific storage var.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.