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 +1,29 @@
+[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"
+# tendermint-proto = "0.34.0"
+tendermint-light-client-verifier = "0.34.0"

crates/test/cometstub/src/lib.rs

@@ -0,0 +1,89 @@
+use tendermint::{
+    abci::{request::BeginBlock, types::CommitInfo},
+    account,
+    block::{Header, Height, Round},
+    chain,
+    validator::Set,
+    AppHash, Hash, Time,
+};
+use tendermint_light_client_verifier::{
+    options::Options,
+    types::{TrustedBlockState, UntrustedBlockState},
+    Verdict, Verifier,
+};
+
+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 },
+        chain_id: chain::Id::try_from("test").unwrap(),
+        height: Height::default(),
+        time: Time::unix_epoch(),
+        last_block_id: None,
+        last_commit_hash: None,
+        data_hash: None,
+        validators_hash: validators().hash(),
+        next_validators_hash: validators().hash(),
+        consensus_hash: Hash::None,
+        app_hash: app_hash(),
+        last_results_hash: None,
+        evidence_hash: None,
+        proposer_address: account::Id::new([
+            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        ]),
+    }
+}
+
+fn validators() -> Set {
+    Set::new(vec![], None)
+}
+
+fn app_hash() -> AppHash {
+    AppHash::try_from(vec![1, 2, 3]).unwrap()
+    // AppHash::try_from is infallible, see: https://github.com/informalsystems/tendermint-rs/issues/1243
+}
+
+pub struct TestVerifier;
+impl Verifier for TestVerifier {
+    fn verify_update_header(
+        &self,
+        _untrusted: UntrustedBlockState<'_>,
+        _trusted: TrustedBlockState<'_>,
+        _options: &Options,
+        _now: Time,
+    ) -> Verdict {
+        todo!("<BarkBark as Verifier>::verify_update_header")
+    }
+    fn verify_misbehaviour_header(
+        &self,
+        _untrusted: UntrustedBlockState<'_>,
+        _trusted: TrustedBlockState<'_>,
+        _options: &Options,
+        _now: Time,
+    ) -> Verdict {
+        todo!("<BarkBark as Verifier>::verify_misbehaviour_header")
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    // use tendermint_light_client_verifier::
+
+    #[test]
+    fn begin_block_works() {
+        let _ = super::begin_block();
+        // next, parse this block via a light client
+    }
+}