RzCore: read core block before printing

[ret2libc]

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• I've added tests that prove my fix is effective or that my feature works (if possible)
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Detailed description

With the new pd conversion to newshell, it seems that those commands directly use core->block, which when setting hardware breakpoints (possibly also in other cases) might be outdated. In general, I think we should try to remove core->block as much as possible and maybe use an internal(transparent) cache within RzCore/RzIo.

Test plan

See issue.

Closing issues

Closes #2692