Problem: memiavl don't support exporting a subtree for execution

## Context

To re-execute a part of stf in zk-prover, we can't load the whole tree in memory, we'll need to find the minimal sub-tree that's enough for the stf execution.

## Solution

for example to prove the execution of a range of blocks `[a, b]`:
1. load memiavl tree at version `a-1`.
2. replay the range of blocks `[a, b]`, and mark the touched nodes (both read and write) whose version `< a`.
3. export those marked nodes.

Start by locating how the memiavl tree is loaded at version a-1 and how the STF replay over blocks [a, b] accesses state. Trace how touched nodes, including reads and writes with versions below a, could be identified and exported. Done means the exported minimal subtree is sufficient to re-execute the selected range without loading the whole tree.

Written by the indexing model from the issue text.