Support converting arrow Interval scalars to Python objects

[kylebarron]

arro3/pyo3-arrow/src/scalar/mod.rs

Lines 314 to 315 in dba93f3

	// https://github.com/apache/arrow-rs/blob/6c59b7637592e4b67b18762b8313f91086c0d5d8/arrow-array/src/temporal_conversions.rs#L219
	todo!("interval is not yet fully documented [ARROW-3097]")

ref apache/arrow#19453