Clean up dead code

[madiator]

Note

Low Risk
Low risk cleanup that removes unused properties/imports and consolidates a cache-dir constant; behavior should be unchanged unless external code relied on the removed APIs.

Overview
Removes unused/dead APIs and imports across the Curator client and response types (drops Client.authenticated, removes CuratorResponse.display_stats and its color constants dependency, and cleans up unused TYPE_CHECKING scaffolding).

Consolidates the _CURATOR_DEFAULT_CACHE_DIR definition by importing it from constants in CodeExecutor instead of maintaining a local duplicate.

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