Implement `__eq__` for `fastcore.xml.FT` for value-based comparison

[gsganden]

Currently, fastcore.xml.FT instances appear to compare by identity rather than value. This behavior can make tasks like testing more complex. For example, fastcore.xml.FT("a", ("b",)) == fastcore.xml.FT("a", ("b",)) comes out False, which requires workarounds such as custom comparison helpers in tests. Implementing an __eq__ method in FT that compares instances based on their tag, attrs, and children would simplify these scenarios by enabling direct, intuitive value-based equality.

This change will require adding a corresponding __hash__ method if these objects are intended to be hashable.

I'm willing to make a PR if desired.