change(state): Add an init function for a standalone ReadStateService

[arya2]

Motivation

We want a function for initializing a ReadStateService

Closes #8520.

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Solution

• Adds init_read_only() and spawn_init_read_only() functions to zebra-state

Testing

Zebra already uses a read-only version of ZebraDb in the scanning results reader binary.

Review

Anyone can review.

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[oxarbitrage]

Looks good and it is working for me, thanks!