Define testing strategy for sdk and env consistency across versions

[leighmcculloch]

Contract behaviors, beyond their own logic, are mostly defined by the host, not by the SDK, because the system is "host heavy" in terms of where functionality lives. The SDK is a very thin layer. It is 99% just changing how a host function is presented, so it looks more like common Rust code. If we intend to test contract behavior consistency outside of the contracts own internal logic, we need to test across all variations of 1) Env versions, 2) a matrix of SDK and Env versions, and 3) a matrix of SDK and SDK versions.

Are there other ways we intend to test Env's participation in consistency?

_Originally posted by @leighmcculloch in stellar/rs-soroban-sdk#1095

We need a test pipeline for testing different combinations of SDK and Env, that also test data persistence across protocol upgrades, SDK upgrades, so as to identify behavior changes in existing APIs prior to a release occurring.