Break out the ASN1 primitives into their own crate or feature?

I'm wondering if it would be possible to break out the ASN1 primitives in the `asn1` folder as their own independent crate or as a feature of the CMS crate that we could use independently? The rest of the crate brings in dependencies that we can't support (notably blocking calls on `reqwest` that can't compile on some of our targeted platforms).

Start by inspecting the `asn1` folder and how it is included by the CMS crate, then identify where the unsupported blocking `reqwest` dependency enters the build. Determine whether the primitives can be independently consumed without those dependencies; done means the chosen crate or feature builds for the targeted platforms and its existing users remain functional.

Written by the indexing model from the issue text.