ndb: remove mutability on transaction reference

It is unnecessary

src/ndb.rs

@@ -80,15 +80,15 @@ impl Ndb {
 
     pub fn get_profile_by_pubkey<'a>(
         &self,
-        transaction: &'a mut Transaction,
+        transaction: &'a Transaction,
         id: &[u8; 32],
     ) -> Result<ProfileRecord<'a>> {
         let mut len: usize = 0;
         let mut primkey: u64 = 0;
 
         let profile_record_ptr = unsafe {
             bindings::ndb_get_profile_by_pubkey(
-                transaction.as_mut_ptr(),
+                transaction.as_ptr() as *mut bindings::ndb_txn,
                 id.as_ptr(),
                 &mut len,
                 &mut primkey,
@@ -112,15 +112,15 @@ impl Ndb {
     /// Get a note from the database. Takes a [Transaction] and a 32-byte [Note] Id
     pub fn get_note_by_id<'a>(
         &self,
-        transaction: &'a mut Transaction,
+        transaction: &'a Transaction,
         id: &[u8; 32],
     ) -> Result<Note<'a>> {
         let mut len: usize = 0;
         let mut primkey: u64 = 0;
 
         let note_ptr = unsafe {
             bindings::ndb_get_note_by_id(
-                transaction.as_mut_ptr(),
+                transaction.as_ptr() as *mut bindings::ndb_txn,
                 id.as_ptr(),
                 &mut len,
                 &mut primkey,

src/note.rs

@@ -80,6 +80,14 @@ impl<'a> Note<'a> {
         }
     }
 
+    /// Get the note pubkey
+    pub fn pubkey(&self) -> &'a [u8; 32] {
+        unsafe {
+            let ptr = bindings::ndb_note_pubkey(self.as_ptr());
+            &*(ptr as *const [u8; 32])
+        }
+    }
+
     pub fn kind(&self) -> u32 {
         unsafe { bindings::ndb_note_kind(self.as_ptr()) }
     }