Now that we have plugin support for Chronik, we can build a plugin to index Agora Oneshot offers efficiently.
Using the /utxos endpoint for the Agora plugin, users can basically fetch the equivalent of an orderbook from the blockchain.
D16551 allows us to use the test_framework's CScript class and all the opcodes.
We have to add a hash160 function; the current impl requires it to be enabled in OpenSSL, but we might add it from ripemd160.py from the test_framework too at some point, or add a function from Rust.
We also add `Agora` and `AgoraOffer` to `ecash-agora`, allowing easy fetching, accepting and cancelling of offers via the plugin, and to have a precise estimation of the required sats.
Depends on D16673.