fix: Make building without client feature work again

[Swatinem]

We weren't testing this in CI previously. And it would seem that this was broken
in the monorepo anyway, since it requires resolver = "2" in order not to unify
features.

supercedes #415, as we still want the API (and trace propagation via headers) to work in such cases.

[codecov-commenter]

Codecov Report

Merging #416 (19495a8) into master (c75d62a) will increase coverage by 0.24%.
The diff coverage is 83.07%.

❗ Current head 19495a8 differs from pull request most recent head f8e2fe3. Consider uploading reports for the commit f8e2fe3 to get more accurate results

@@            Coverage Diff             @@
##           master     #416      +/-   ##
==========================================
+ Coverage   82.37%   82.62%   +0.24%     
==========================================
  Files          70       70              
  Lines        7950     7983      +33     
==========================================
+ Hits         6549     6596      +47     
+ Misses       1401     1387      -14