Clang-tidy fixes

[knoepfel]

Built on top of the configuration changes at #102.

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 20 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
phlex/model/level_counter.cpp	0.00%	4 Missing ⚠️
phlex/model/level_hierarchy.cpp	20.00%	4 Missing ⚠️
phlex/utilities/resource_usage.cpp	20.00%	4 Missing ⚠️
phlex/core/declared_predicate.hpp	91.30%	1 Missing and 1 partial ⚠️
phlex/core/declared_unfold.hpp	93.75%	1 Missing and 1 partial ⚠️
phlex/app/load_module.cpp	50.00%	0 Missing and 1 partial ⚠️
phlex/core/declared_fold.hpp	88.88%	1 Missing ⚠️
phlex/core/detail/filter_impl.cpp	0.00%	0 Missing and 1 partial ⚠️
phlex/model/algorithm_name.cpp	50.00%	1 Missing ⚠️

@@            Coverage Diff             @@
##             main     #101      +/-   ##
==========================================
- Coverage   81.67%   81.56%   -0.12%     
==========================================
  Files         118      119       +1     
  Lines        2074     2105      +31     
  Branches      336      336              
==========================================
+ Hits         1694     1717      +23     
- Misses        244      255      +11     
+ Partials      136      133       -3     

Flag	Coverage Δ
unittests	81.56% <87.50%> (-0.12%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
phlex/configuration.hpp	100.00% <100.00%> (ø)
phlex/core/consumer.cpp	60.00% <ø> (ø)
phlex/core/declared_observer.hpp	100.00% <100.00%> (ø)
phlex/core/declared_transform.hpp	91.48% <100.00%> (+0.18%)	⬆️
phlex/core/detail/filter_impl.hpp	100.00% <ø> (ø)
phlex/core/dot/attributes.cpp	100.00% <ø> (ø)
phlex/core/dot/attributes.hpp	100.00% <100.00%> (ø)
phlex/core/dot/data_graph.cpp	97.46% <100.00%> (ø)
phlex/core/dot/function_graph.cpp	100.00% <100.00%> (ø)
phlex/core/edge_maker.hpp	94.64% <100.00%> (ø)
... and 42 more

... and 1 file with indirect coverage changes

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