Expose JSON Schema ID and maturity as class methods

[korikuzma]

As I have began working on the starter kit and bundle format for civicpy, I need a way to resolve the schema identifiers.

For example,

{
  "$id": "https://w3id.org/ga4gh/schema/vrs/2.1.0-snapshot.2026-02.2/json/Allele",
  "maturity": "trial use"
}

I imagine others will want this too. It'd be useful to expose this info through class methods, like the following:

Allele.schema_id()
# "https://w3id.org/ga4gh/schema/vrs/2.1.0-snapshot.2026-02.2/json/Allele"

Allele.maturity()
# "trial use"