Take the value of `CHECKPOINT_ADDRESS` (rename to: `REVERT_ROOT_HASH`) from emulator.

[mpolitzer]

This value is hard coded as of #241. It should be dictated by the emulator from v0.20 going forward.

Rust code can bind the value from: machine/emulator/src/machine-c-api.h
Lua code can retrieve it from:

cm = require'cartesi'
cm.AR_SHADOW_REVERT_ROOT_HASH_START