Use Vec::from_iter in Buffer::from_iter

[Kikkon]

Which issue does this PR close?

Closes #4937 .

Rationale for this change

What changes are included in this PR?

Replace unsafe code with Vec::from_iter in Buffer::from_iter for improved safety and performance

Are there any user-facing changes?

no

[tustvold]

Have you run any benchmarks to confirm this doesn't regress performance. The arithmetic kernels might be a good candidate

[Kikkon]

@tustvold Thanks for your advice, I will first change it to the draft status. I will reopen it after I have finished supplementing the benchmark.

[Kikkon]

Hi @tustvold ,
After comparing with the baseline on the master branch, it appears that this change has no impact on performance. If there are no other concerns, perhaps it's ready for merging. By the way, are there any other issues suitable for newcomers? I think I might not be very familiar with this area yet. (:

[tustvold]

I did a scan of this and it turns out we don't use this code for anything other than tests anymore, instead preferring either the trusted length or unary/binary methods

any other issues suitable for newcomers?

#5445 should be straightforward