Fix conversion to Protocol Buffers of ClientState's frozen_height field

[hu55a1n1]

Closes: cosmos/ibc-rs#62

Description

The fix in #1640 was incomplete, so we basically needed to make sure that we serialize domain type frozen height None as Some(Height::zero()), because that's what ibc-go expects.

---

PR author checklist:

• Added changelog entry, using unclog.
• Added tests: integration (for Hermes) or unit/mock tests (for modules).
• Linked to GitHub issue.
• Updated code comments and documentation (e.g., docs/).

Reviewer checklist:

• Reviewed Files changed in the GitHub PR explorer.
• Manually tested (in case integration/unit/mock tests are absent).

[hu55a1n1]

To test with basecoin-rs ->

1. Checkout the hu55a1n1/module-verification branch
2. Apply the following diff to disable connection proof verification (that I'm yet to fix) ->

diff --git a/modules/src/core/ics03_connection/handler/verify.rs b/modules/src/core/ics03_connection/handler/verify.rs
index 917fb5ac..e6485ef6 100644
--- a/modules/src/core/ics03_connection/handler/verify.rs
+++ b/modules/src/core/ics03_connection/handler/verify.rs
@@ -16,17 +16,17 @@ pub fn verify_proofs(
     client_state: Option<AnyClientState>,
     height: Height,
     connection_end: &ConnectionEnd,
-    expected_conn: &ConnectionEnd,
+    _expected_conn: &ConnectionEnd,
     proofs: &Proofs,
 ) -> Result<(), Error> {
-    verify_connection_proof(
-        ctx,
-        height,
-        connection_end,
-        expected_conn,
-        proofs.height(),
-        proofs.object_proof(),
-    )?;
+    // verify_connection_proof(
+    //     ctx,
+    //     height,
+    //     connection_end,
+    //     expected_conn,
+    //     proofs.height(),
+    //     proofs.object_proof(),
+    // )?;
 
     // If the message includes a client state, then verify the proof for that state.
     if let Some(expected_client_state) = client_state {

3. Try to create a connection between the basecoin chain and a gaia chain using these instructions -> Phase4 basecoin-rs#20 (comment)