Update Rust dependencies

[lucarlig]

Summary

• refresh Rust dependencies with Cargo's breaking-update flow followed by a full compatible lockfile update
• inherit direct dependencies from [workspace.dependencies] when at least two members use them, while keeping single-member dependencies local
• enforce shared dependency inheritance and reject unused workspace entries with cargo-deny
• remove the avoidable second itertools version by replacing its four sorting helpers with the standard library
• migrate to RMCP 2.2 using commit 3252f013 from the merged enabling_propagation_of_new_session_id_2 fork branch
• fix progress routing so an immediate backend notification cannot overtake publication of RMCP's generated-token mapping
• make progress tests use distinct string downstream tokens and update the request-flow documentation

RMCP migration

The migration follows the RMCP 2.x guide, including ContentBlock, flat resource types, builders, response enums, and generated progress-token behavior. The exact pin targets commit 3252f013 on the merged enabling_propagation_of_new_session_id_2 branch, including the initialize-session correction.