Re-structure sat-rs

- Add new shared subcrate satrs-shared to split off some shared
  components not expected to change very often.
- Renmame `satrs-core` to `satrs`. It is expected that sat-rs will remain
  the primary crate, so the core information is superfluous, and core also
  implies stability, which will not be the case for some time.

satrs-example/src/udp.rs

@@ -4,7 +4,7 @@ use std::{
 };
 
 use log::{info, warn};
-use satrs_core::{
+use satrs::{
     hal::std::udp_server::{ReceiveResult, UdpTcServer},
     pool::{PoolProviderWithGuards, SharedStaticMemoryPool, StoreAddr},
     tmtc::CcsdsError,
@@ -113,7 +113,7 @@ mod tests {
         sync::{Arc, Mutex},
     };
 
-    use satrs_core::{
+    use satrs::{
         spacepackets::{
             ecss::{tc::PusTcCreator, WritablePusPacket},
             SpHeader,