Add rsl::StrongType

[ChrisThrasher]

Strong type aliases are a useful pattern but they require just enough boilerplate that you don't typically see codebases implement them and they're just small and non-specific enough that libraries don't provide them. This type aims to fill that gap so that we can actually use strong type aliases in our code.

Motivating example:

using JointID = rsl::StrongType<std::uint64_t, struct JointIDTag>;

struct Joint {
    JointID id;
    int count;
};

auto joint = Joint{JointID(4), 2};
auto joint = Joint{2, JointID(4)}; // Won't compile

The presence of a strong type alias ensures that the order of arguments is correct. Without that strong alias, it would be easy to accidentally swap the two arguments without realizing it.

[codecov]

Codecov Report

Merging #87 (9296fdc) into main (5c0d774) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #87      +/-   ##
==========================================
+ Coverage   99.05%   99.06%   +0.01%     
==========================================
  Files          10       11       +1     
  Lines         211      215       +4     
==========================================
+ Hits          209      213       +4     
  Misses          2        2              

Flag	Coverage Δ
humble	99.06% <100.00%> (+0.01%)	⬆️
rolling	99.06% <100.00%> (+0.01%)	⬆️

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Files	Coverage Δ
include/rsl/strong_type.hpp	100.00% <100.00%> (ø)

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[ChrisThrasher]

I added constexpr support along with tests with non-constexpr types to confirm everything still works.

[ChrisThrasher]

Added missing Doxygen comments