feat(interop): introduce field-mask context for u5c (#502)

pallas-utxorpc/src/lib.rs

@@ -5,6 +5,7 @@ use pallas_crypto::hash::Hash;
 use pallas_primitives::{alonzo, babbage, conway};
 use pallas_traverse as trv;
 
+use prost_types::FieldMask;
 use trv::OriginalHash;
 
 pub use utxorpc_spec::utxorpc::v1alpha as spec;
@@ -25,12 +26,22 @@ pub trait LedgerContext: Clone {
 #[derive(Default, Clone)]
 pub struct Mapper<C: LedgerContext> {
     ledger: Option<C>,
+    mask: FieldMask,
 }
 
 impl<C: LedgerContext> Mapper<C> {
     pub fn new(ledger: C) -> Self {
         Self {
             ledger: Some(ledger),
+            mask: FieldMask { paths: vec![] },
+        }
+    }
+
+    /// Creates a clone of this mapper using a custom field mask
+    pub fn masked(&self, mask: FieldMask) -> Self {
+        Self {
+            ledger: self.ledger.clone(),
+            mask,
         }
     }
 }