[MISC] relax kmer_hash_view::iterator difference requirement

[marehr]

The difference operator on iterators only needs the requirement std::sized_sentinel_for<it_t, it_t>, i.e. the underlying iterator has a difference operator, instead of the full std::random_access_iterator.

The random_access_iterator requires that as a subclause

    std::totally_ordered<I> &&
    std::sized_sentinel_for<I, I> && // here
    requires(I i, const I j, const std::iter_difference_t<I> n) {

An example from the standard would be here: https://eel.is/c++draft/range.adaptors#range.transform.iterator-22 where it also only requires std::sized_sentinel_for.

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[codecov]

Codecov Report

Merging #2931 (137891f) into master (f668060) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2931   +/-   ##
=======================================
  Coverage   98.28%   98.28%           
=======================================
  Files         267      267           
  Lines       11462    11462           
=======================================
  Hits        11265    11265           
  Misses        197      197           

Impacted Files	Coverage Δ
include/seqan3/search/views/kmer_hash.hpp	100.00% <ø> (ø)

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[smehringer]

Makes sense since we only compute the difference and this concept checks "whether you can compute the distance".

I guess this holds for more of our views but I would alter them if the use case arises.

[marehr]

I guess this holds for more of our views but I would alter them if the use case arises.

We could still make this a follow-up easy to-do issue. Searching for operator- and checking whether the iterator difference operator has the right restriction, shouldn't be too hard.