ini/unstable: Add option to collect repeated key/values into arrays

**Is your feature request related to a problem? Please describe.**

Most of the config standards I work with that use ini-based configs all have repeated key/value entries for various options, and with the removal of [`IniMap`](https://github.com/denoland/std/pull/6515#issuecomment-2785738781) in the unstable versions, there won't be a good option for parsing those ini's using a package on JSR.

**Describe the solution you'd like**

A simple option

**Describe alternatives you've considered**

Staying on the old version