fix(versioning): replace session-state guard with InvalidRequestError catch

The previous attempt (d0520f6766) was too aggressive: skipping when
parent is in session.dirty/new/deleted bypassed the
persistent-and-clean case the hook EXISTS for. Some upstream code
paths put the dataset in session.dirty *before* this listener fires
(API controllers touching audit fields, etc.), so the
session-membership pre-check made us silently no-op on the very
scenario the hook needs to handle. CI symptom:
test_dataset_column_edit_creates_parent_version showed before=317,
after=317 (parent shadow not written).

Restore the unconditional flag_modified and catch the specific
InvalidRequestError that fires only for the session.new case
(uuid default callable hasn't populated state yet). Other states
fall through to the original behavior:
- persistent + clean → flag_modified succeeds, parent goes dirty,
  Continuum picks it up, SkipUnmodifiedPlugin keeps the row via
  _has_dirty_versioned_children. ✓
- persistent + dirty → flag_modified is harmless (already dirty).
- session.new → InvalidRequestError, skip (parent INSERTs anyway).
- session.deleted → flag_modified may or may not raise; if it does,
  we skip; if not, the delete dominates.

Should unblock test_dataset_column_edit_creates_parent_version,
test_get_version_returns_historical_snapshot_with_children, and
test_restore_with_column_edits_reverts_columns.