Bump version to 0.3.4 and add a Fabric install note: deltalake is preloaded by the
runtime, so `%pip install duckrun --upgrade` only takes effect after
`notebookutils.session.restartPython()` — that restart is what swaps in the pinned
deltalake 1.5.0.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>