v0.20.0

This release explicitly targets Hubuum server v0.0.21. Upgrade the server before
using field discovery or schema suggestions.

Added

• Bounded field discovery by class ID, exact name, or class handle in async and
  blocking clients. Validated options preserve structured paths, sampled counts,
  computed-field sources, previews, and truncation without downloading objects.
• Typed schema profiling requests, task discovery, retained reports, and a
  submit/wait/fetch suggestion helper. Reviewed candidates feed explicit staging;
  whole-class impact analysis and activation remain separate actions. Failed,
  cancelled, expired, and inaccessible work retains actionable errors.
• Coverage of the server's profiling execution timeout in administrator settings.

Changed

• Breaking: TaskDetails adds schema_profiling. Existing complete struct
  literals must add schema_profiling: None or use ..Default::default();
  exhaustive patterns must bind the new field or add ...
  Existing deserialization and accessors continue to accept older responses.
• Target Hubuum server v0.0.21 and its 261-operation contract. Refresh compatible
  dependencies while retaining Rust 1.88 and the existing public feature sets.