hvtiBoostmtree 2.0.1

Patch release. Two plotting label/length fixes found via a codebase review (both pre-existing, inherited from upstream kogalur/boostmtree; neither affects model fitting or numeric output).

Bug Fixes

• vimpPlot() no longer over-supplies bar labels. The internal graphics::text() calls passed rep(xvar.names, 3) — three labels for every bar — which triggered a 'labels' truncated to length ... warning and could mislabel bars. Labels now correspond one-to-one with the plotted bars.
• plot.boostmtree() now draws the optimal-iteration reference line for every class of a multiclass (Nominal/Ordinal) prediction object. The internal abline() calls indexed an already-scalar Mopt as Mopt[q], yielding NA (and a silently missing line) for the second and later classes.

Both fixes ship with red→green regression tests. Release gate: R CMD check --as-cran with PDF manual = 0 errors / 0 warnings / 1 benign NOTE.

Additional review findings tracked as issues #8–#15.