Cosmos gas price config (#3042)

### Description

Adds a cosmos-specific config item for setting the minimum gas price, in
the format returned by the `cosmos.base.node.v1beta1.Service/Config`
cosmos-sdk grpc endpoint.

### Related issues

- Fixes hyperlane-xyz/issues#810

### Backward compatibility

No. Will break existing cosmos configs.


### Testing

None yet, will test in e2e

.github/ISSUE_TEMPLATE/feature_request.md

@@ -4,7 +4,6 @@ about: Suggest an idea for this project
 title: ''
 labels: ''
 assignees: ''
-
 ---
 
 ## Problem

rust/Cargo.toml

@@ -55,6 +55,7 @@ async-trait = "0.1"
 auto_impl = "1.0"
 backtrace = "0.3"
 base64 = "0.21.2"
+bigdecimal = "0.4.2"
 bincode = "1.3"
 borsh = "0.9"
 bs58 = "0.5.0"

rust/agents/relayer/Cargo.toml

@@ -39,6 +39,7 @@ hyperlane-base = { path = "../../hyperlane-base" }
 hyperlane-ethereum = { path = "../../chains/hyperlane-ethereum" }
 
 [dev-dependencies]
+once_cell.workspace = true
 tokio-test.workspace = true
 hyperlane-test = { path = "../../hyperlane-test" }
 hyperlane-base = { path = "../../hyperlane-base", features = ["test-utils"] }

rust/agents/relayer/src/msg/gas_payment/mod.rs

@@ -4,8 +4,8 @@ use async_trait::async_trait;
 use eyre::Result;
 use hyperlane_base::db::HyperlaneRocksDB;
 use hyperlane_core::{
-    GasPaymentKey, HyperlaneMessage, InterchainGasExpenditure, InterchainGasPayment,
-    TxCostEstimate, TxOutcome, U256,
+    FixedPointNumber, GasPaymentKey, HyperlaneMessage, InterchainGasExpenditure,
+    InterchainGasPayment, TxCostEstimate, TxOutcome, U256,
 };
 use tracing::{debug, error, trace};
 
@@ -135,7 +135,8 @@ impl GasPaymentEnforcer {
         self.db.process_gas_expenditure(InterchainGasExpenditure {
             message_id: message.id(),
             gas_used: outcome.gas_used,
-            tokens_used: outcome.gas_used * outcome.gas_price,
+            tokens_used: (FixedPointNumber::try_from(outcome.gas_used)? * outcome.gas_price)
+                .try_into()?,
         })?;
         Ok(())
     }

rust/agents/relayer/src/msg/gas_payment/policies/minimum.rs

@@ -59,7 +59,7 @@ async fn test_gas_payment_policy_minimum() {
                 &current_expenditure,
                 &TxCostEstimate {
                     gas_limit: U256::from(100000u32),
-                    gas_price: U256::from(100000u32),
+                    gas_price: U256::from(100000u32).try_into().unwrap(),
                     l2_gas_limit: None,
                 },
             )
@@ -83,7 +83,7 @@ async fn test_gas_payment_policy_minimum() {
                 &current_expenditure,
                 &TxCostEstimate {
                     gas_limit: U256::from(100000u32),
-                    gas_price: U256::from(100001u32),
+                    gas_price: U256::from(100001u32).try_into().unwrap(),
                     l2_gas_limit: None,
                 },
             )
@@ -101,7 +101,7 @@ async fn test_gas_payment_policy_minimum() {
                 &current_expenditure,
                 &TxCostEstimate {
                     gas_limit: U256::from(100000u32),
-                    gas_price: U256::from(100001u32),
+                    gas_price: U256::from(100001u32).try_into().unwrap(),
                     l2_gas_limit: Some(U256::from(22222u32)),
                 },
             )