datasource/cpan: use module API instead of file

[rarkins]

Discussed in #37518

^{Originally posted by oalders August 14, 2025}

Tell us more.

This is a follow-on from #37238

Renovate is using a custom query rather than an official API to find latest modules. For example, Data::Calc can be looked up via https://fastapi.metacpan.org/v1/module/Date::Calc rather than using a custom query. The module endpoint already takes into account the various edge cases that can come up when looking for the latest version of a module.