Fix some PhantomData declarations

Specify the expected type instead of () even if only the lifetime
matters

src/backup.rs

@@ -165,8 +165,8 @@ pub struct Progress {
 
 /// `feature = "backup"` A handle to an online backup.
 pub struct Backup<'a, 'b> {
-    phantom_from: PhantomData<&'a ()>,
-    phantom_to: PhantomData<&'b ()>,
+    phantom_from: PhantomData<&'a Connection>,
+    phantom_to: PhantomData<&'b Connection>,
     b: *mut ffi::sqlite3_backup,
 }
 

src/session.rs

@@ -22,7 +22,7 @@ use crate::{errmsg_to_string, str_to_cstring, Connection, DatabaseName, Result};
 /// `feature = "session"` An instance of this object is a session that can be
 /// used to record changes to a database.
 pub struct Session<'conn> {
-    phantom: PhantomData<&'conn ()>,
+    phantom: PhantomData<&'conn Connection>,
     s: *mut ffi::sqlite3_session,
     filter: Option<Box<dyn Fn(&str) -> bool>>,
 }
@@ -299,7 +299,7 @@ impl Drop for Changeset {
 /// `feature = "session"` Cursor for iterating over the elements of a changeset
 /// or patchset.
 pub struct ChangesetIter<'changeset> {
-    phantom: PhantomData<&'changeset ()>,
+    phantom: PhantomData<&'changeset Changeset>,
     it: *mut ffi::sqlite3_changeset_iter,
     item: Option<ChangesetItem>,
 }