Added high-level abstraction for some PUS services

Introduced high-level abstractions for targetable requests in general.

- PUS Service 3 (HK) abstraction for targetable HK requests
- PUS Service 8 (Action) abstraction for targetable action requests

satrs/src/cfdp/dest.rs

@@ -23,7 +23,7 @@ use spacepackets::{
         tlv::{msg_to_user::MsgToUserTlv, EntityIdTlv, GenericTlv, TlvType},
         ChecksumType, ConditionCode, FaultHandlerCode, PduType, TransmissionMode,
     },
-    util::UnsignedByteField,
+    util::{UnsignedByteField, UnsignedEnum},
 };
 use thiserror::Error;