implement oldest newest and near methods in the cdx interface class, now cli uses the cdx methods instead of availablity api methods.

tests/test_cdx_snapshot.py

@@ -41,3 +41,4 @@ def test_CDXSnapshot() -> None:
     )
     assert archive_url == snapshot.archive_url
     assert sample_input == str(snapshot)
+    assert sample_input == repr(snapshot)