Add nullifier epoch verification to transaction prologue

[bobbinth]

To support epoch-based nullifier scheme, we need to verify a mapping between nullifier and an epoch index as described in 0xPolygonMiden/miden-vm#356 (comment). This will require the following changes:

• Compute the nullifier commitment as a sequential hash of (nullifier, script_root, epoch_index) tuples (vs. current (nullifier, script_root).
• In the prologue, compute epoch index for each nullifier. Epoch index can be computed based on the block number in which the note was create - but we still need to figure out the exact parameters.
• Verify that the computed epoch index is greater than or equal to the epoch index provided via the nullifier commitment.

[Dominik1999]

Should we hold off on this? According to our latest discussion, we might not need to introduce epochs at the beginning.

#106

[Dominik1999]

Should we not introduce epochs of nullifiers for now? I wanted to update the docs.

[bobbinth]

I think we should mention the epoch-based nullifier in the docs as technical people would wonder how we are planning to deal with nullifier DB growth (which would be a real problem for a high TPS system). So, basically, we may hold off on implementing this, but the docs should probably describe the approach (and we can say that initially, we'll have a simplified version of this).