[meawoppl]

Heyo, I am doing some work to get our sweet (astronomy centric) plotting tools out in the wild. This seemed like a nice entry point, and I thought I might probe your interest in future contributions here...

This ports celestial-pointing/src/plot/svg.rs from plotters to rizzma, a pure-Rust plotting library modelled on matplotlib. The public functions (scatter_svg, histogram_svg, vector_map_svg) keep their signatures, so no callers change, and the textplots terminal renderer is untouched.

What each command draws now:

• GSCAT / GHA / GDEC / GHYST: the same residual scatter plots, with the zero crosshairs drawn as axhline/axvline instead of path segments.
• GDIST: hist_with(…, 20 bins) replaces the hand-written binning, which is deleted. Bin counts are identical to before, and the grid sits behind the bars.
• GMAP: residuals are real arrows with heads (quiver_with, in data units) instead of bare line segments. The [scale] argument still works: an arrow runs from each position to position + scale × residual.

Checked with pointing-data/gem-28.dat (454 observations, fit with IH ID CH NP MA ME): every plot has the expected number of points, bars and arrows, and all 600 crate tests pass. Clippy is clean with -D warnings.

Trade-offs, to be upfront:

• The dependency tree grows, because rizzma brings a rasteriser and font parser even when only SVG is written. plotters' SVG backend is lighter.
• The SVGs are a little larger than plotters' (GSCAT: 85 KB vs 61 KB), mainly because text is drawn as outlines. Setting rizzma's svg_fonttype to native text cuts GSCAT to about 33 KB, half of plotters', if you'd prefer that; it's a one-line change.

Happy to adjust styling, or to hold this if you'd rather keep the lighter SVG backend.