Implement Electrum Protocol v1.6

[tnull]

Closes #189.

I asked Claude Code to implement the changes necessary to update to the recently released Electrum Protocol v1.6.

Putting in draft for now until I got initial feedback (cc @oleonardolima @ValuedMammal). We also still need to change the test setup to a v1.6-compatible server to actually run the new tests against.

[tnull]

Hmm, test_local_timeout is currently failing, likely because we now need to successfully negotiate the version before returning the client. Though I have to say I don't fully understand what the test is for in the first place. Could someone explain what we try to assert there exactly?

[ValuedMammal]

Concept ACK

[tnull]

Alright, now updated the CI to use a v1.6 server for tests, fixed some minor things that came up, and opted to simply drop the test_local_timeouts test case as its dummy server implementation is incompatible with the v1.6 flow (that requires version negotiation). Let me know if you think that's acceptable @oleonardolima @ValuedMammal.

Undrafted, as this should be ready-to-go.

[ValuedMammal]

I did a first pass, overall it looks reasonable. I left some nits and a few questions. I'm curious if you've had a chance to test this in the wild.

In 38386fe: "feat: Automatically negotiate protocol version on connect"

The commit message refers to a server_version() method that "updates the stored version", but that seems to be hallucinated.

[tnull]

I did a first pass, overall it looks reasonable. I left some nits and a few questions. I'm curious if you've had a chance to test this in the wild.

No, we did not test this in the wild yet, though of course now the tests run against v1.6 mainnet servers, so they are somewhat an 'in the wild' test.

The commit message refers to a server_version() method that "updates the stored version", but that seems to be hallucinated.

Ah, not hallucinated, but this is a stale comment that referred to a previous approach that I ended up amending.

[tnull]

Addressed pending comments and force-pushed the following changes:

> git diff-tree -U2  485c4b0 a439485
diff --git a/src/raw_client.rs b/src/raw_client.rs
index d806a92..3feb754 100644
--- a/src/raw_client.rs
+++ b/src/raw_client.rs
@@ -47,5 +47,5 @@ use crate::types::*;

 /// Client name sent to the server during protocol version negotiation.
-pub const CLIENT_NAME: &str = "rust-electrum-client";
+pub const CLIENT_NAME: &str = "";

 /// Minimum protocol version supported by this client.
@@ -965,4 +965,5 @@ impl<T: Read + Write> ElectrumApi for RawClient<T> {
                 deserialized.headers.push(deserialize(&header_bytes)?);
             }
+            deserialized.header_hexes.clear();
             Ok(deserialized)
         } else {