various fixes and updates for satrs-core

1. Fix pools integration test to avoid occasional deadlocks
2. tmtc module: The `CcsdsPacketHandler` and `PusServiceProvider`
   do not require a send bound anymore. However, these traits now
   have an extension trait called `Sendable<DefaultName>` which requires
   the trait + Send. A blanket implementation is provided. The helper
   structs like `PusDistributor` and `CcsdsDistributor` require
   the new Sendable trait version to allow more ergnomic usage
   with threads.

satrs-core/tests/pools.rs

@@ -20,14 +20,15 @@ fn threaded_usage() {
     });
 
     let jh1 = thread::spawn(move || {
-        let mut pool_access = shared_clone.write().unwrap();
         let addr;
         {
             addr = rx.recv().expect("Receiving store address failed");
+            let mut pool_access = shared_clone.write().unwrap();
             let pg = PoolGuard::new(pool_access.deref_mut(), addr);
             let read_res = pg.read().expect("Reading failed");
             assert_eq!(read_res, DUMMY_DATA);
         }
+        let pool_access = shared_clone.read().unwrap();
         assert!(!pool_access.has_element_at(&addr).expect("Invalid address"));
     });
     jh0.join().unwrap();