* Implement styled arguments
* Inherit from formatter<Arg> to get the underlying `parse` and `format`
* Move styled_arg definition into the previous detail block
* Change styled_arg ctor parameters names to avoid shadowing members
* Move const before auto
* Remove redundant constructor for styled_arg
* Use the iterator instead of the buffer in styled_arg::format
* Remove unnecessary `styled` overloads
* Remove defaulted text_style parameter in styled function
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