cbor: allow user to control nesting (#329)

* cbor: allow user to control nesting

 - Make the default read/write entrypoints allow infinite nesting.
 - Add {read,write}_nested() entrypoints that allow the crate user to
   control the depth of nesting that's allowed.
 - Along the way, convert the write[_nested] variants to return a
   `Result<(), EncoderError>` rather than a bool.  This exposes
   more failure information (and forces the caller to take notice
   of those tailures), and allows use of the ? operator.

* fixup: transmute error

Co-authored-by: kaczmarczyck <43844792+kaczmarczyck@users.noreply.github.com>

libraries/cbor/src/values.rs

@@ -130,9 +130,9 @@ impl Ord for Value {
             (v1, v2) => {
                 // This case could handle all of the above as well. Checking individually is faster.
                 let mut encoding1 = Vec::new();
-                write(v1.clone(), &mut encoding1);
+                let _ = write(v1.clone(), &mut encoding1);
                 let mut encoding2 = Vec::new();
-                write(v2.clone(), &mut encoding2);
+                let _ = write(v2.clone(), &mut encoding2);
                 encoding1.cmp(&encoding2)
             }
         }