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

[yihuang]

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.