feat: namespaces

Right now the read path is scanning all transactions matching the script template we're using in the write path. So it's sort of permissionless but we don't have a namespaces yet. We could support namespaces by having an address derive from the namespace and updating the read path to accept the namespace, this also improves the reliability of the read path as it doesn't have to do template matching on the witness script, which is a bit flaky.