Avoid lambdas in class template static member initializers (MSVC)

[stephenberry]

MSVC intermittently fails to compile beve_test: it resolves the immediately invoked lambda in BEVE's object writer (beve/write.hpp) to the lambda in meta<std::tuple<...>>::name's initializer, an unrelated closure type (C3889, then C3536). The BEVE code has not changed; the failure comes and goes across unrelated PRs.

This removes immediately invoked lambdas from the static data member initializers of class templates, the pattern MSVC confused:

• meta<std::tuple>, meta<std::variant> and meta<glz::tuple> build their names with a new comma_separated_names_v<T...> variable template.
• trait<T>::members uses a detail::trait_member_names<T>() function.

The generated names and API hashes (glz::hash<T>()) are unchanged.