Address issues with rustc 1.65

[glandium]

Fixes #30

[baumanj]

I'm pretty sure there are other places where the isize::MAX limit of allocations needs updating (like tryhashmap_oom). It might be worth making a crate-level constant like MAX_ALLOCATION = isize::MAX as usize and using that as a point to explain the limit and link to supporting documentation.

[baumanj]

I recognize this matches the existing code, but it strikes me as odd to use a match here rather than a simple assert like

Suggested change

	match FallibleVec::try_reserve(&mut vec, core::usize::MAX / std::mem::size_of::<char>()) {
	Ok(_) => panic!("it should be OOM"),
	_ => (),
	}
	assert!(FallibleVec::try_reserve(&mut vec, core::usize::MAX / std::mem::size_of::<char>()).is_err());

For the sake of clarity, it seems worth changing both to the more idiomatic approach.

Also, based on https://rust-lang.github.io/unsafe-code-guidelines/layout/scalars.html#isize-and-usize, should this be testing the tighter bound of isize::MAX?