Fixes masp tx generation and integration tests

crates/namada/src/ledger/protocol/mod.rs

@@ -691,7 +691,11 @@ where
         .expect("Missing masp fee payment gas limit in storage")
         .min(tx_gas_meter.borrow().tx_gas_limit.into());
 
-    let mut gas_meter = TxGasMeter::new(min_gas_limit);
+    let mut gas_meter = TxGasMeter::new(
+        namada_gas::Gas::from_whole_units(min_gas_limit).ok_or_else(|| {
+            Error::GasError("Overflow in gas expansion".to_string())
+        })?,
+    );
     gas_meter
         .copy_consumed_gas_from(&tx_gas_meter.borrow())
         .map_err(|e| Error::GasError(e.to_string()))?;

crates/sdk/src/args.rs

@@ -2138,9 +2138,6 @@ pub struct Tx<C: NamadaTypes = SdkTypes> {
     pub gas_limit: GasLimit,
     /// The optional expiration of the transaction
     pub expiration: TxExpiration,
-    // FIXME: maybe should move this out of here, it's only needed for txs that
-    // pay the fees via the masp, so it should go together with the optional
-    // gas spending keys
     /// Generate an ephimeral signing key to be used only once to sign a
     /// wrapper tx
     pub disposable_signing_key: bool,

crates/sdk/src/error.rs

@@ -264,7 +264,10 @@ pub enum TxSubmitError {
     #[error("Proposal end epoch is not in the storage.")]
     EpochNotInStorage,
     /// Couldn't understand who the fee payer is
-    #[error("Either --signing-keys or --gas-payer must be available.")]
+    #[error(
+        "Either --signing-keys, --gas-payer or --disposable-gas-payer must be \
+         available."
+    )]
     InvalidFeePayer,
     /// Account threshold is not set
     #[error("Account threshold must be set.")]