0.30 release

[davidhewitt]

While the 0.29 release is not yet out the door, there have been a few topics which have been notable but not quite ready to ship in 0.29. I wanted to list these here now so that we can avoid forgetting these as we work towards 0.30.

• list iterator issues list iterator implementation doesn't match Python semantics #6087
• migrate to PyClassGuard from PyRef - PyRefMut::as_super and PyClassGuardMut::as_super enable type confusion #6083
  • deprecate PyRef(Mut) (Part 1) #6120
  • deprecate Bound|Py::(try_)borrow(_mut) (Part 2) #6121
• OverflowError / ValueError consistency - negative-to-unsigned conversions are inconsistent between ValueError and OverflowError #6116, Python-to-rust conversion of integer raises an OverflowError instead of ValueError when value is out of bounds #5179
• build performance - Make pyo3-build-config more caching friendly #6113