fix!: Fix type equality between arro3 and pyarrow

[kylebarron]

#462 looked like it should've been a simple refactor for nicer code, but it actually created #482, because the derived equality checking from pyo3 doesn't use the Arrow PyCapsule extraction. So it would only check for equality with other pyo3 objects, not any Arrow-like object.

This PR reverts #462 and adds tests that we can assert equality for all types (except for the lazy readers) with PyArrow.

The other part of equality that was biting me was #451, since I incorrectly was taking in references, not owned types.

Unfortunately, part of this change is that we now export DataType with nullable: true instead of nullable: false, so we probably need to put this in a new minor release, not a bugfix release.

Change list

• Revert refactor(pyo3-arrow): Use simpler derived eq for python __eq__ duner #462
• Add tests for equality of all types. Python's __eq__ calls the left side first. So ideally anyone who wants to compare arro3 types to other types should put the arro3 types first. This works reflexively with pyarrow for most types, because pyarrow returns NotImplemented, which then tells Python to check the other direction for equality. This doesn't work for RecordBatch because apparently PyArrow has some custom __eq__ there.
• We also now export a bare DataType through __arrow_c_schema__ with nullable: true, which was required to match equality semantics with pyarrow.

Reverts #462, Closes #482