Limit visibility of id method for SessionContext to the crate only

Because SessionContext itself is limited in visibility to the crate this
id method should also be lmited to crate visibility.

Author: benalleng

payjoin/src/receive/v2/mod.rs

@@ -58,7 +58,7 @@ impl SessionContext {
     }
 
     /// The per-session identifier
-    pub fn id(&self) -> ShortId {
+    pub(crate) fn id(&self) -> ShortId {
         sha256::Hash::hash(&self.s.public_key().to_compressed_bytes()).into()
     }
 }