[MISC] use new CPO-way to define seqan3::assign_phred_to

[marehr]

Part of seqan/product_backlog#298.

[vercel]

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[codecov]

Codecov Report

Merging #2476 (33d83c0) into master (e616011) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2476   +/-   ##
=======================================
  Coverage   98.30%   98.30%           
=======================================
  Files         267      268    +1     
  Lines       11063    11063           
=======================================
  Hits        10875    10875           
  Misses        188      188           

Impacted Files	Coverage Δ
include/seqan3/alphabet/quality/concept.hpp	100.00% <100.00%> (ø)
include/seqan3/core/detail/customisation_point.hpp	100.00% <0.00%> (ø)

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[simonsasse]

Looks good :)