Allows calling cmdl.params( { "--name", "-n" } ) and getting all relevant values, regardless of which param name was used on the command line. For example,

std::ranges::for_each(
   cmdl.params( { "--name", "-n" } ) | std::views::values,
   []( const std::string& value ) {
      // do something with the parameter value
    } );

Since the implementation uses std::ranges, perhaps it's a good idea to conditionally enable it only for c++>=20 and feature test __cpp_lib_ranges; I know some projects prefer making equivalent tests in the build system and setting a compiler definition accordingly, any thoughts?

Also, this implementation requires that the parser's lifetime exceeds that of the return value -- this gets captured in the lambda -- which to me seems natural in most use cases, and a reasonable thing to require (and document). The alternative would be making a copy of the data...