Introduce Customization struct (#458)

* Introduce Customization trait

* Introduce Customization trait including the customization accessors
  that control various behaviors.

* Expose Customization through a getter API in Env, and make the code
  that directly access the constants currently switch to accessing the
  customizations via Env.

* TockEnv's customization getter implementation directly returns the
  reference of the global DEFAULT_CUSTOMIZATION constant, so the
  constant values are still inlined and dead code won't be compiled.

* We'll add the customizations from global constants to the struct
  one-by-one, only MAX_MSG_SIZE in this commit.

* Small fixes

* Fix deploy script
* put is_valid under std gate

src/ctap/customization.rs

@@ -119,15 +119,6 @@ pub const ENTERPRISE_ATTESTATION_MODE: Option<EnterpriseAttestationMode> = None;
 /// VendorFacilitated.
 pub const ENTERPRISE_RP_ID_LIST: &[&str] = &[];
 
-/// Maximum message size send for CTAP commands.
-///
-/// The maximum value is 7609, as HID packets can not encode longer messages.
-/// 1024 is the default mentioned in the authenticatorLargeBlobs commands.
-/// Larger values are preferred, as that allows more parameters in commands.
-/// If long commands are too unreliable on your hardware, consider decreasing
-/// this value.
-pub const MAX_MSG_SIZE: usize = 7609;
-
 /// Sets the number of consecutive failed PINs before blocking interaction.
 ///
 /// # Invariant
@@ -252,8 +243,6 @@ mod test {
         } else {
             assert!(ENTERPRISE_RP_ID_LIST.is_empty());
         }
-        assert!(MAX_MSG_SIZE >= 1024);
-        assert!(MAX_MSG_SIZE <= 7609);
         assert!(MAX_PIN_RETRIES <= 8);
         assert!(MAX_CRED_BLOB_LENGTH >= 32);
         if let Some(count) = MAX_CREDENTIAL_COUNT_IN_LIST {