[theminjunchoi]

What this PR does / why we need it:

Fixes #147

interop/run.py now runs every case with and without TLS, so the job goes from 112 runs to 224. The Go and Python clients connect to 127.0.0.1 and verify the certificate as localhost. The summary shows one table for each.

tests/test_tls.py gets handshake tests that connect with Python's ssl. They cover TLS 1.2 and 1.3, a client that doesn't offer h2, and required client certificates on TLS 1.2. Both grpcio and pygrpc-native have to give the same result.

The job now also fails when empty_unary fails on grpcio. Before, a client that couldn't connect failed on both servers, and that counted as no difference.

How it was tested:

All 224 interop runs pass, and so does pytest tests. tests/test_tls.py also passes on Python 3.10 with grpcio 1.64.3, and on 3.13.

To check the tests can fail, I broke src/server/tls.rs three ways:

Change	New tests	Existing tests	Interop
No ALPN	1 fails	12 fail	50 runs fail
No client certificate check	2 fail	9 fail	passes
TLS 1.3 only	2 fail	pass	passes

Pointing the clients at the wrong CA fails the job too.

Special notes for your reviewers:

Most of the interop/run.py diff is indentation from the new loop.

A client that offers no ALPN isn't tested on purpose, because the two servers differ there: see #146.

If applicable:

• this PR changes user-facing behavior, and the README is updated
• this PR contains tests