Get Validation Plot Data

Return decimated trace data for a single validation or data-fit plot.

Reads the stored validation_plot_config from the job's metadata blob, extracts the requested plot, filters to the given x-range, and downsamples to at most max_points per trace. Supports semantic zoom: callers refetch with x_min/x_max set to the current viewport on each zoom event.

max_points is a per-trace ceiling, and a figure may hold several traces, so it is reduced where the whole response would otherwise exceed the payload cap — see src.jobs.plot_data._payload_capped_budget.