v0.19.4

Adds

• markersPossible on SeriesChart: the hint row keeps the room of the hint with markers, so the chart does not move when trades come and go.
• SeriesHintRow: the same row for a loading stand-in, with the hint held unseen and hidden from screen readers.

Changes

• The hint row holds its hint unseen under the readout, so inspecting a point no longer shortens it.
• A chart whose plot fails to load keeps the held hint row.