fix some GCC warnings and update codecov

[phlptp]

Try to address some of the warnings that have been reported from GCC.

[codecov]

Codecov Report

Base: 99.42% // Head: 99.44% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (02cc628) compared to base (71755e4).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #813      +/-   ##
==========================================
+ Coverage   99.42%   99.44%   +0.01%     
==========================================
  Files          16       16              
  Lines        3991     3950      -41     
==========================================
- Hits         3968     3928      -40     
+ Misses         23       22       -1     

Impacted Files	Coverage Δ
include/CLI/App.hpp	100.00% <ø> (ø)
include/CLI/Validators.hpp	99.30% <0.00%> (-0.70%)	⬇️
include/CLI/impl/StringTools_inl.hpp	95.42% <0.00%> (-0.09%)	⬇️
include/CLI/impl/Validators_inl.hpp	99.50% <0.00%> (-0.02%)	⬇️
include/CLI/impl/Option_inl.hpp	99.74% <0.00%> (-0.01%)	⬇️
include/CLI/Error.hpp	100.00% <0.00%> (ø)
include/CLI/Timer.hpp	100.00% <0.00%> (ø)
include/CLI/Option.hpp	100.00% <0.00%> (ø)
include/CLI/ConfigFwd.hpp	100.00% <0.00%> (ø)
... and 6 more

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[phlptp]

Fixes the redundant declaration warnings from #805