Remove @always_bls decorator

[dzhalaevd]

Description

Remove @always_bls decorator from the pyspec test suite and from docs

closes: #5032
related: #5015

Todo

• Update documentation
• Run make lint to check formatting
• Run make test to check tests

[brech1]

I'm afraid removing @always_bls also drops bls_setting: 1 from the generated test vectors, and this breaks clients test harnesses that rely on it to gate BLS verification.

This needs to be part of a broader bls_setting and never_bls restructure, not a standalone removal.

The best would be to postpone this change, any update on this decorator or bls_settings would need client teams coordination too. Thank you for working on it, didn't realize this when creating the issue 🙏