Add new decorators to skip tests and handle it in testgen

[hwwhww]

Sorry, 3 different parts in this PR.

Issue 1 (minor)

get_custody_secret is duplicate.

Solution for Issue 1

Use v-guide's get_custody_secret in test helper.

---

Issue 2

For some test cases, it can't be passed with mainnet configs.

Solution for Issue 2

1. Add with_configs decorator to assign available configs
2. Add only_full_crosslink decorator to detect if the configuration can
   do full crosslinking: some test cases assume that each slot has enough committee to form crosslink.
3. Add CONFIG_NAME to the config files. "mainnet" or "minimal".

---

Issue 3

1. Test generator calls test case without pytest.
2. Devs and CI use pytest to run the tests.

It would be better to handle the "unavailable" forks and configs properly. e.g., some test cases are only for phase 0, or some test cases are only for mainnet configs.

Solution for Issue 3

1. Add context.is_pytest flag: True if calling via pytest. False if calling from test generator.

2. Add dump_skipping_message to dump message to pytest caller or test generator runner:

   def dump_skipping_message(reason: str) -> None:
       message = f"[Skipped test] {reason}"
       if is_pytest:
           pytest.skip(message)
       else:
           raise SkippedTest(message)

   • If it's for pytest: mark it is skip. For example, if we call pytest --disable-bls --config=mainnet eth2spec/test/phase1/sanity/test_blocks.py, it will show some test cases are skipped:

   

   • If it's called by test generator, the SkippedTest exception will be caught and show message like:

   Generating test: output/minimal/phase1/sanity/blocks/pyspec_tests/multiple_different_validator_exits_same_block
   [Skipped test] doesn't support this fork: phase1
   

3. Add pytest to gen_helpers requirements. But note that it's just because pytest is imported in eth2spec/test/context.py, the test generator does NOT use it.

[djrtwo]

well done!

[protolambda]

Nice work! Changes look good, but there are a few older tests where the test had to be skipped. Updating these to raise the new SkippedTest would be best I think.

[protolambda]

LGTM