feat(wallet_ffi): new ffi method to create covenant (#4115)

Description
---
* Created a new FFI method to create a covenant object from bytes.
* Updated the C header with the definition of the new method

Motivation and Context
---
Currently the mobile apps cannot properly import faucet UTXOs, as they are passing null values for output features and covenants to the `wallet_import_external_utxo_as_non_rewindable` method, which is not allowed. So the mobile apps needs new FFI methods to create both output features and covenants. This pull request deals with covenants only.

How Has This Been Tested?
---
Created two new unit tests for the new FFI method

base_layer/wallet_ffi/src/lib.rs

@@ -990,7 +990,63 @@ pub unsafe extern "C" fn commitment_signature_destroy(com_sig: *mut TariCommitme
 }
 
 /// -------------------------------------------------------------------------------------------- ///
+/// --------------------------------------- Covenant --------------------------------------------///
 
+/// Creates a TariCovenant from a ByteVector containing the covenant bytes
+///
+/// ## Arguments
+/// `covenant_bytes` - The covenant bytes as a ByteVector
+///
+/// ## Returns
+/// `TariCovenant` - Returns a commitment signature. Note that it will be ptr::null_mut() if any argument is
+/// null or if there was an error with the contents of bytes
+///
+/// # Safety
+/// The ```covenant_destroy``` function must be called when finished with a TariCovenant to prevent a memory leak
+#[no_mangle]
+pub unsafe extern "C" fn covenant_create_from_bytes(
+    covenant_bytes: *const ByteVector,
+    error_out: *mut c_int,
+) -> *mut TariCovenant {
+    let mut error = 0;
+    ptr::swap(error_out, &mut error as *mut c_int);
+
+    if covenant_bytes.is_null() {
+        error = LibWalletError::from(InterfaceError::NullError("covenant_bytes".to_string())).code;
+        ptr::swap(error_out, &mut error as *mut c_int);
+        return ptr::null_mut();
+    }
+    let decoded_covenant_bytes = (*covenant_bytes).0.clone();
+
+    match TariCovenant::from_bytes(&decoded_covenant_bytes) {
+        Ok(covenant) => Box::into_raw(Box::new(covenant)),
+        Err(e) => {
+            error!(target: LOG_TARGET, "Error creating a Covenant: {:?}", e);
+            error = LibWalletError::from(InterfaceError::InvalidArgument("covenant_bytes".to_string())).code;
+            ptr::swap(error_out, &mut error as *mut c_int);
+            ptr::null_mut()
+        },
+    }
+}
+
+/// Frees memory for a TariCovenant
+///
+/// ## Arguments
+/// `covenant` - The pointer to a TariCovenant
+///
+/// ## Returns
+/// `()` - Does not return a value, equivalent to void in C
+///
+/// # Safety
+/// None
+#[no_mangle]
+pub unsafe extern "C" fn covenant_destroy(covenant: *mut TariCovenant) {
+    if !covenant.is_null() {
+        Box::from_raw(covenant);
+    }
+}
+
+/// -------------------------------------------------------------------------------------------- ///
 /// ---------------------------------- Output Features ------------------------------------------///
 
 /// Creates a TariOutputFeatures from byte values
@@ -6585,7 +6641,10 @@ mod test {
 
     use libc::{c_char, c_uchar, c_uint};
     use tari_common_types::{emoji, transaction::TransactionStatus};
-    use tari_core::transactions::test_helpers::{create_unblinded_output, TestParams};
+    use tari_core::{
+        covenant,
+        transactions::test_helpers::{create_unblinded_output, TestParams},
+    };
     use tari_key_manager::{mnemonic::MnemonicLanguage, mnemonic_wordlists};
     use tari_test_utils::random;
     use tari_wallet::{
@@ -7094,6 +7153,42 @@ mod test {
         }
     }
 
+    #[test]
+    fn test_covenant_create_empty() {
+        unsafe {
+            let mut error = 0;
+            let error_ptr = &mut error as *mut c_int;
+
+            let covenant_bytes = Box::into_raw(Box::new(ByteVector(Vec::new())));
+            let covenant = covenant_create_from_bytes(covenant_bytes, error_ptr);
+
+            assert_eq!(error, 0);
+            let empty_covenant = covenant!();
+            assert_eq!(*covenant, empty_covenant);
+
+            covenant_destroy(covenant);
+            byte_vector_destroy(covenant_bytes);
+        }
+    }
+
+    #[test]
+    fn test_covenant_create_filled() {
+        unsafe {
+            let mut error = 0;
+            let error_ptr = &mut error as *mut c_int;
+
+            let expected_covenant = covenant!(identity());
+            let covenant_bytes = Box::into_raw(Box::new(ByteVector(expected_covenant.to_bytes())));
+            let covenant = covenant_create_from_bytes(covenant_bytes, error_ptr);
+
+            assert_eq!(error, 0);
+            assert_eq!(*covenant, expected_covenant);
+
+            covenant_destroy(covenant);
+            byte_vector_destroy(covenant_bytes);
+        }
+    }
+
     #[test]
     fn test_output_features_create_empty() {
         unsafe {

base_layer/wallet_ffi/wallet.h

@@ -189,6 +189,17 @@ struct TariCommitmentSignature *commitment_signature_create_from_bytes(
 // Frees memory for a TariCommitmentSignature
 void commitment_signature_destroy(struct TariCommitmentSignature *com_sig);
 
+/// -------------------------------- Covenant  --------------------------------------------- ///
+
+// Creates a TariCovenant from a ByteVector containing the covenant bytes
+struct TariCovenant *covenant_create_from_bytes(
+    struct ByteVector *covenant_bytes,
+    int *error_out
+);
+
+// Frees memory for a TariCovenant
+void covenant_destroy(struct TariCovenant *covenant);
+
 /// -------------------------------- Output Features  --------------------------------------------- ///
 
 // Creates a TariOutputFeatures from byte values