cleanup: fix GCC warnings with Wall

[coryan]

I was too optimistic about the state of the code with GCC 13, while the code is clean with Clang, there was a useful warning emited by GCC 13, and a number of useless warnings too.

[codecov[bot]]

Codecov Report

Merging #395 (986303f) into main (6fabe85) will not change coverage. The diff coverage is 100.00%.

:exclamation: Current head 986303f differs from pull request most recent head 89b5b24. Consider uploading reports for the commit 89b5b24 to get more accurate results

@@           Coverage Diff           @@
##             main     #395   +/-   ##
=======================================
  Coverage   89.40%   89.40%           
=======================================
  Files          97       97           
  Lines        3133     3133           
=======================================
  Hits         2801     2801           
  Misses        332      332           

Impacted Files	Coverage Δ
examples/site/http_content/http_content.cc	97.91% <100.00%> (ø)

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