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/mod.rs

@@ -9,7 +9,7 @@ use spacepackets::{
         pdu::{FileDirectiveType, PduError, PduHeader},
         ChecksumType, ConditionCode, FaultHandlerCode, PduType, TransmissionMode,
     },
-    util::UnsignedByteField,
+    util::{UnsignedByteField, UnsignedEnum},
 };
 
 #[cfg(feature = "alloc")]