Public data reads and update requests in public kernel

[sirasistant]

For a given TX, after its public kernel executions:

• All public data reads should refer to the state previous to the tx. All other public data reads are transient and can be simplified out.
• The public data writes should at most write once per slot. All duplicated writes can be simplified out and leave just the last one.
• The public data writes exposed to the base rollup should not include the old value, since it won't verify the old value. It's fine to use it as a hint to the public kernel.