[WIP/WORKING TREE] V1.2.0

[turtle261]

Begin refactor for maintainability and extensibility in the expected development trajectory.

Done already:

1. Restructure repository root to be less intimidating.
2. Make it so development of new RateBackends is DRY
3. Feature gate all RateBackends, so you may optionally only pay for what you use (primarily to address binary size)
4. Improve the benchmarking framework: now includes faster regression tests. So each commit will no longer require an 8 hour comprehensive re-evaluation, and that can be left for releases or version increments.
5. Improve test comprehensiveness significantly. Will Cross-reference against the many papers for which we claim to implement or just do implement, and Rigorously prove bounds/identities/invariants, etc.
6. Add GameEngine as the default environment layer, including replacing the builtin in paper games such as Kuhn poker into GameEngine Games -- with strictly proven properties to replace the current games are a brainfuck to audit. Infotheory will at that point support: 1. GameEngine described games. On Linux, full Linux environments via Nyx-lite. 3. And manually implemented environment types, whether it be in Rust or Python (if one wants too). This would be a functional change.
7. Importantly, unify specifications for RateBackends, AIXI configuration, environments, etc -- all as Struct or Enum-based, and a universal encoder/decoder to support JSON, but also compiling that into a minimal and non-human readable bitpacked representation, which will be necessary for future features, and so configs aren't several KBs unnecessarily. This is functional change 2.
8. Reduce planner/runtime branching duplication (kind of a functional change)
9. Govern public surface and remove duplicate entry points.
10. Improve accountability of information and control over determinism

Repository/workspace restructure: Converts the root Cargo.toml into a workspace-only manifest, moving main crates under crates/*, relocating submodules under vendor/* (including new vendor/gameengine), and bumping crate versions to 1.2.0.