Proposal: Access extension by MIME type string

[surkaa]

Context

Currently, infer maintains an internal MATCHER_MAP with MIME types and extensions, but it's private.

The Problem

Sometimes I already have a MIME string (e.g., from an HTTP header) and want the extension. Currently, I have to add a heavy dependency like mime_guess even though the data already exists inside infer.

Proposed Solution

Expose a simple lookup function or make the matchers iterator public.

Example:

let ext = infer::get_extension("image/jpeg"); // returns Some("jpg")