add Bound API constructors from borrowed pointers

[davidhewitt]

As per #3708 (comment)

I decided to add both Bound::from_borrowed_ptr and Borrowed::from_ptr sets of methods. I think the Bound methods make sense from a consistency with Py angle and also for simplicity. The Borrowed methods may be useful in extreme cases for power users, and also are what I'd like to use internally in #3708

[codspeed-hq]

CodSpeed Performance Report

Merging #3858 will degrade performances by 20.41%

_{Comparing davidhewitt:borrowed-ptrs (bc53537) with main (5f42c02)}

Summary

⚡ 3 improvements
❌ 1 regressions
✅ 75 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	davidhewitt:borrowed-ptrs	Change
⚡	f64_from_pyobject	516.7 ns	405.6 ns	+27.4%
⚡	list_via_downcast	185 ns	157.2 ns	+17.67%
⚡	list_via_extract	364.4 ns	308.9 ns	+17.99%
❌	not_a_list_via_downcast	216.7 ns	272.2 ns	-20.41%

[Icxolu]

It seems reasonable to me, that we add both Bound and Borrowed variants. Found a small documentation mixup, otherwise LGTM

[Icxolu]

Suggested change

	/// Constructs a new `Borrowed<'py, PyAny>` from a pointer. Panics if `ptr` is null.
	/// Constructs a new `Borrowed<'a, 'py, PyAny>` from a pointer. Returns an `Err` by calling `PyErr::fetch`
	/// if `ptr` is null.

Missing lifetime here, same for the others. Also you mixed the or_err and panicking variants

[davidhewitt]

Good catch. I think I got mixed up because the functions aren't in the same order as for Bound - I'll swap them so that from_ptr is first at the same time 👍

[davidhewitt]

Thanks for the review, will try to fixup tonight 👍