Increase version counter to `2025-1`

[arnoweiss]

Before a first Release Candidate, the version should be incremented to 2025-1. This affects the spec text, formatting and URIs.

Discussed in #74

^{Originally posted by arnoweiss November 28, 2024}
There's a couple of release-related issues I'm anticipating for the upcoming works.

1. artifacts: message schemas, the @context etc may require a new release and thus get new identifiers.
2. Do we need specification text in the releases folder?
3. there's files namespaced as belonging to a certain release which weren't in initially. That may motivate a new release. (see Context Schema doesn't resolve #76)