feat: merkle tree support

[anxolin]

For now, we are focusing on single order, and get TWAP indexing to work as smooth as possible

After that we will need to deprecate the old validation done in watch tower and move the logic to the SDK.

For now, we keep a simple approach, where each conditional order type implementation implements a isSingleOrder: boolean accessor that will signal that is not a Merkle root order.

This issue is to improve our Merkle root order (and potentially delete this prop)