rename `current_span_len()` to something better

[dvdsk]

we should rename current_span_len() to samples_left_in_span() or something better. The current name sounds like the length is fixed, it can however be called at any time and then should returns the samples left until the resample rate and/or channel count can change. That is better communicated by having the word "left" in the name. Adding the word "samples" to the name makes it clear its not the number of frames.

Originally posted by @dvdsk in #684 (comment)

[PetrGlad]

Yes, It makes sense. Ideally this should be counted in frames, not samples, but that requires rewriting algorithms, including ones that users may already have...

Could it be remaining_span_samples?

[dvdsk]

Could it be remaining_span_samples?

for me samples_left_in_span is clearer, what do you like about remaining_span_samples? Yet another alternative would be samples_remaining_in_span.

[PetrGlad]

I would not insist on this option. Just hoped that there is something that is more concise. Identifiers do not need to be proper phrases.

[dvdsk]

Identifiers do not need to be proper phrases.

I find code more readable when they are, but I do not know if there is consensus on that. Ill have to look into best practices for variable naming. If I find any we can make that a guideline for the project. Only if we both agree it of course.

[dvdsk]

closed in favor of #694