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>

src/ctap/credential_management.rs

@@ -30,7 +30,6 @@ use alloc::vec::Vec;
 use crypto::sha256::Sha256;
 use crypto::Hash256;
 use libtock_drivers::timer::ClockValue;
-use sk_cbor as cbor;
 
 /// Generates a set with all existing RP IDs.
 fn get_stored_rp_ids(
@@ -289,9 +288,7 @@ pub fn process_credential_management(
                 pin_uv_auth_protocol.ok_or(Ctap2StatusCode::CTAP2_ERR_MISSING_PARAMETER)?;
             let mut management_data = vec![sub_command as u8];
             if let Some(sub_command_params) = sub_command_params.clone() {
-                if !cbor::write(sub_command_params.into(), &mut management_data) {
-                    return Err(Ctap2StatusCode::CTAP2_ERR_VENDOR_INTERNAL_ERROR);
-                }
+                super::cbor_write(sub_command_params.into(), &mut management_data)?;
             }
             client_pin.verify_pin_uv_auth_token(
                 &management_data,