RunEngine documentation and execution diagrams updated

Developers working with the RunEngine now have access to an accurate, up-to-date architectural reference. A native ASCII flow chart has been added to the documentation, cleanly detailing the precise lifecycle of a run from trigger and queuing to execution and completion. The platform's conceptual documentation has also been aligned with recent system changes: references to self-hosted worker groups have been entirely replaced with regions, and the legacy waitpoint concepts have been swapped out for the new token-based wait APIs. Sections covering deprecated or moved features like throttling and batching have been removed, ensuring the documentation only presents currently supported capabilities.