feat: 📝 implement cometstub crate (work-in-progress)

this commit introduces a new library, in `crates/test/`. this library
contains a mock implementation of cometbft, for use in cargo integration
tests.

* this does NOT add the `penumbra-cometstub` crate to the list of
  crates included in the rust documentation in
  `deployments/scripts/rust-docs`. the `penumbra-tct-property-test`
  crate was also not included in that list at the time of writing.

/!\ ------------------------------------------------------- /!\
/!\ NOTE: this is a rolling work-in-progress.               /!\
/!\ this branch will be force-pushed frequently until it is /!\
/!\ ready for review. proceed accordingly!                  /!\
/!\ ------------------------------------------------------- /!\

Cargo.toml

@@ -43,6 +43,7 @@ members = [
   "crates/bin/pclientd",
   "crates/bin/pcli",
   "crates/wasm",
+  "crates/test/cometstub",
   "crates/test/tct-property-test",
   "crates/misc/measure",
   "crates/misc/tct-visualize",

crates/test/cometstub/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "penumbra-cometstub"
+version = "0.64.1"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[features]
+default = ["component", "std"]
+component = [
+    # "cnidarium",
+    # "cnidarium-component",
+    # "penumbra-proto/cnidarium",
+    # "penumbra-chain/component",
+]
+std = ["ibc-types/std"]
+
+[dependencies]
+# Workspace dependencies
+
+# Penumbra dependencies
+ibc-proto = { version = "0.40.0", default-features = false }
+ibc-types = { version = "0.11.0", default-features = false }
+
+# Crates.io deps
+anyhow = "1"
+tendermint = "0.34.0"

crates/test/cometstub/src/lib.rs

@@ -0,0 +1,67 @@
+use tendermint::{
+    abci::types::CommitInfo,
+    block::{Header, Round, Height},
+    Hash, Time,
+};
+use {
+    ibc_proto::{
+        google::protobuf::Any, ibc::core::client::v1::MsgCreateClient as RawMsgCreateClient,
+    },
+    ibc_types::{core::client::msgs::MsgCreateClient, DomainType},
+    tendermint::abci::request::BeginBlock,
+};
+
+pub fn begin_block() -> BeginBlock {
+    BeginBlock {
+        hash: Hash::None,
+        header: header(),
+        last_commit_info: CommitInfo {
+            round: Round::default(),
+            votes: vec![],
+        },
+        byzantine_validators: vec![],
+    }
+}
+
+fn header() -> Header {
+    use tendermint::block::header::Version;
+    Header {
+        version: Version { block: 0, app: 0 },              //: Version,
+        chain_id: todo!(),             //: chain::Id,
+        height: Height::default(),               //: block::Height,
+        time: Time::unix_epoch(),                 //: Time,
+        last_block_id: None,        //: Option<block::Id>,
+        last_commit_hash: None,     //: Option<Hash>,
+        data_hash: None,            //: Option<Hash>,
+        validators_hash: todo!(),      //: Hash,
+        next_validators_hash: todo!(), //: Hash,
+        consensus_hash: todo!(),       //: Hash,
+        app_hash: todo!(),             //: AppHash,
+        last_results_hash: None,    //: Option<Hash>,
+        evidence_hash: None,        //: Option<Hash>,
+        proposer_address: todo!(),     //: account::Id,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use {
+        super::*,
+        ibc_types::{core::client::msgs::MsgCreateClient, DomainType},
+    };
+
+    #[test]
+    fn begin_block_works() {
+        let msg = begin_block();
+        unimplemented!("generate a begin block message")
+    }
+}
+
+// TODO(katie): this sketch is loosely based upon test_create_and_update_light_client. i am not
+// convinced this is the right direction quite yet. i see very little interaction with headers
+// themselves, it feels vaguely like we should be generating abci messages instead?
+//
+// Any is another puzzle. how to make those?
+//
+// tendermint_proxy contains the logic to marshal a tendermint::Block into its
+// protobuf representation. consider moving that, see the todo comment there.