Define ordering across heterogeneous EndPoint implementations

[dkropachev]

Problem

EndPoint subclasses implement __lt__ assuming the other operand has the same concrete type. Directly sorting heterogeneous endpoints can therefore fail.

from cassandra.connection import DefaultEndPoint, UnixSocketEndPoint

UnixSocketEndPoint('/tmp/cql.sock') < DefaultEndPoint('127.0.0.1')

This raises AttributeError because UnixSocketEndPoint.__lt__ reads _unix_socket_path from the DefaultEndPoint. The reverse comparison can also raise TypeError when tuple comparison reaches an integer port versus None.

The behavior predates PR #944. That PR only adds deterministic mixed ordering at the Host layer and should not broaden into a public endpoint-ordering redesign. Found while reviewing #944 (comment).

Expected behavior

Define and document one cross-type ordering contract for built-in endpoint implementations, or make heterogeneous comparison explicitly unsupported and ensure callers use a shared sort key.

Acceptance criteria

• Comparing or sorting heterogeneous built-in endpoints does not fail unexpectedly.
• Default, Unix socket, SNI, and Client Routes endpoints are covered.
• Equality, hashing, and ordering remain internally consistent.