For CardBackend and CardTransaction, implement T for Box<T>

- Allow a Box<dyn CardBackend> to be used in all contexts where a
    type that implements CardBackend can be used.

  - Likewise for CardTransaction.

openpgp-card/Cargo.toml

@@ -12,6 +12,7 @@ repository = "https://gitlab.com/hkos/openpgp-card"
 documentation = "https://docs.rs/crate/openpgp-card"
 
 [dependencies]
+blanket = "0.2.0"
 nom = "6"
 hex-literal = "0.3"
 hex-slice = "0.1"

openpgp-card/src/lib.rs

@@ -55,6 +55,7 @@ use crate::tlv::tag::Tag;
 use crate::tlv::value::Value;
 use crate::tlv::Tlv;
 
+#[blanket::blanket(derive(Box))]
 pub trait CardBackend {
     fn transaction(
         &mut self,
@@ -67,6 +68,7 @@ pub trait CardBackend {
 /// after opening a transaction from a CardBackend.
 ///
 /// CardTransaction exposes low-level access to OpenPGP card functionality.
+#[blanket::blanket(derive(Box))]
 pub trait CardTransaction {
     /// Transmit the command data in `cmd` to the card.
     ///