test: reduce parameter selection

[johubertj]

Description of changes:

1. Keep ALL_TEST_CERTS as is
2. only test_happy_path.py will use ALL_TEST_CERTS (preserve coverage)
3. all other tests will use MINIMAL_TEST_CERTS
4. add ECDSA_521 to MINIMAL_TEST_CERTS to ensure coverage over all key types.

Problem:

This PR reduces the number of certificates used in integration tests, limiting them to only the minimal required set, except for test_happy_path.py, which retains all certs for comprehensive coverage. This change optimizes test execution time.

After making the above changes, tests take 9 seconds to complete!

   9781 test_buffered_send.py
   2588 test_signature_algorithms.py
   2000 test_happy_path.py
   1999 test_external_psk.py
   1724 test_session_resumption.py
   1682 test_client_authentication.py
   1525 test_version_negotiation.py
   1275 test_renegotiate.py
   1275 test_npn.py
   1144 test_early_data.py
    864 test_cross_compatibility.py
    576 test_ocsp.py
    300 test_dynamic_record_sizes.py
    271 test_record_padding.py
    127 test_hello_retry_requests.py
     88 test_sni_match.py
     75 test_sslyze.py
     72 test_fragmentation.py
     28 test_renegotiate_apache.py
     15 test_pq_handshake.py
      8 test_serialization.py
      7 test_key_update.py
      1 test_well_known_endpoints.py
      1 test_sslv2_client_hello.py
      1 27426/240090 tests collected (212664 deselected) in 9.76s

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[dougch]

Neat, spot checked one of the aarch64 jobs, run time reduced from 35min to 19min.

[jmayclin]

Could you include the diff in the collected tests in the PR description? before/after. test_happy_path.py seems oddly low ...