shielded-pool: add event creation functions for transfers

Separate commit to make backporting easier.

crates/core/component/shielded-pool/src/event.rs

@@ -1,8 +1,8 @@
 use penumbra_asset::Value;
 use penumbra_keys::Address;
 use penumbra_proto::core::component::shielded_pool::v1::{
-    EventInboundFungibleTokenTransfer, EventOutboundFungibleTokenRefund,
-    EventOutboundFungibleTokenTransfer, EventOutput, EventSpend,
+    event_outbound_fungible_token_refund::Reason, EventInboundFungibleTokenTransfer,
+    EventOutboundFungibleTokenRefund, EventOutboundFungibleTokenTransfer, EventOutput, EventSpend,
 };
 use penumbra_sct::Nullifier;
 
@@ -35,6 +35,30 @@ pub fn outbound_fungible_token_transfer(
     }
 }
 
+#[derive(Clone, Copy, Debug)]
+pub enum FungibleTokenRefundReason {
+    Timeout,
+    Error,
+}
+
+pub fn outbound_fungible_token_refund(
+    value: Value,
+    sender: Address,
+    receiver: String,
+    reason: FungibleTokenRefundReason,
+) -> EventOutboundFungibleTokenRefund {
+    let reason = match reason {
+        FungibleTokenRefundReason::Timeout => Reason::Timeout,
+        FungibleTokenRefundReason::Error => Reason::Error,
+    };
+    EventOutboundFungibleTokenRefund {
+        value: Some(value.into()),
+        sender: Some(sender.into()),
+        receiver,
+        reason: reason as i32,
+    }
+}
+
 pub fn inbound_fungible_token_transfer(
     value: Value,
     sender: String,