internal: Fix double copy creating PyBackedBytes from PyByteArray

[PeterFaiman]

Arc::<[u8]>::from(py_bytearray.to_vec()) creates a Vec copy of the PyByteArray contents, then immediately copies that Vec into an Arc<[u8]>. It should copy the PyByteArray contents directly into the Arc<[u8]>. This PR inlines PyByteArrayMethods::to_vec into PyBackedBytes::from without the unnecessary copy.

pyo3/src/types/bytearray.rs

Lines 291 to 300 in 7550783

	fn to_vec(&self) -> Vec<u8> {
	with_critical_section(self, || {
	// SAFETY:
	// * `self` is a `Bound` object, which guarantees that the Python GIL is held.
	// * For free-threaded Python, a critical section is used in lieu of the GIL.
	// * We don't interact with the interpreter
	// * We don't mutate the underlying slice
	unsafe { self.as_bytes() }.to_vec()
	})
	}

[davidhewitt]

Thanks, seems fine to me!