Django's condition() decorator invokes etag_func and last_modified_func
separately, and the view itself may resolve again -- each call to
resolve_effective_document_by_pk() was redoing the same root/version
DB lookups. Memoize the resolution on the request object so a single
thumb/metadata/preview request resolves the effective document once
instead of up to three times.
Related to paperless-ngx/paperless-ngx#13161.
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
* Adds ETag and Last-Modified headers to suggestions, metadata and previews
* Slight update to the suggestions etag
* Small user message for why classifier didn't train again