v0.18.1

Fixed

• A validation failure inside a dict[str, T] or tuple[T, ...] field of
  Models or tagged unions now carries the element's dict key or list index in
  ValidationErrorEntry.loc, at every depth and on both the model_validate
  and model_validate_json paths, so a bad dev entry of a datasets map
  reports ("datasets", "dev", "corruption") instead of
  ("datasets", "corruption"). (#88)
• didactic-settings composition accepts a tagged-union root as the schema:
  the document's discriminator selects the variant exactly as it does at a
  union-typed field, and a document with no tag is refused at settle with the
  registered tags instead of rejecting the discriminator as an unknown key.
  (#89)