[PoC] Use Esplora for fee estimation and tx broadcast for blocksonly nodes

[kristapsk]

Proof of concept, not for merging at current state.

See #1466. This allows to run JoinMarket with Bitcoin node configured in blocksonly mode (no local mempool). It fallbacks to Esplora (blockstream.info) for fee estimation, which locally will not work at all, and also tries to push tx to the network through it too, not local node, for privacy reasons.

So far have tested with direct (non coinjoin) sends on a testnet3 (unfortunatelly Blockstream doesn't run signet instance of Esplora and https://explorer.bc-2.jp/ which everyone used for signet is down for some time).

Currently this is kinda hacky, Esplora code should not be integrated into blockchaininterface, some refactorizations would be needed. But first I would want to finish with #1462.

[kristapsk]

Did coinjoin test as a taker. It works, just with one nuance - sendpayment.py waits until tx gets first confirmation and only then quits.

[kristapsk]

From #1466 (comment), to not forget.

We should also be careful how we connect to the block explorer, if we reuse the same circuit for multiple broadcast we would reveal (possible) common ownership to the server.

Yes, it should switch Tor circuits, especially when running yield generator. That needs to be improved in my PoC code.

[kristapsk]

Rebased against master to re-run CI with latest fixes.

[kristapsk]

Rebased

[kristapsk]

Rebased

[kristapsk]

Rebased.

Waiting for more concept ACKs / NACKs here, before doing any more work on this.

[kristapsk]

Rebased

[kristapsk]

Rebased

[kristapsk]

Re-added missing PySocks dependency (otherwise SOCKS proxy for requests doesn't work), it was lost at rebase after moving from setup.py to pyproject.toml.

Btw, https://explorer.bc-2.jp for signet is back online, but not usable for JoinMarket, it's requests can't get though CloudFlare DDoS protection.