refactor: remove versioning in the extension crate

[chungquantin]

Versioning is currently handled inside the extension crate for POP API shared between runtimes. However, I find it's a bit weird. In the future, if we have more versions like v1 or v2.

The StateRead logic must be reused and extended (or overwritten completely) for the future versions because the implementation of the extension crate right now only accepts one method read() to handle the state queries, used for v0 and supposed to be used for other versions as well.

This issue can be visited later when we had the introduction of the new versions. Link to the original discussion:

• refactor: generic extension crate to de-duplicate code between runtimes #163 (comment)
• refactor: generic extension crate to de-duplicate code between runtimes #163 (comment)