Render SmartArt diagrams and charts instead of dropping them

[ikashapov]

Render SmartArt diagrams and charts instead of dropping them

Closes #155. Based on main (b2c0174, v0.5.1); one commit, branch
issue-155-smartart-charts. Independent of the other open branches.

Both are DrawingML parts referenced from a:graphicData, and both died at
the same seam: the graphicData schema knew only pic and wsp, so a
dgm:relIds or c:chart child parsed to graphic = None and the drawing
vanished — no space reserved, nothing drawn, not even a warning.

SmartArt — render the baked layout, not the algorithm

The issue guessed SmartArt "may need routing more than new rendering", and
that is exactly how it lands. Word ≥ 2007 SP2 writes a dsp: drawing
part ([MS-ODRAWXML]) into every SmartArt — "the last successful layout of
the diagram": literal shapes with baked fills and fitted text, in absolute
EMU on a canvas the size of the hosting wp:extent. LibreOffice's own
import uses it and throws its approximate layout engine's result away when
it's present; implementing §21.4's layout algorithm instead is a
multi-year effort that would still be approximate. So: parse the part,
route it through the existing shape pipeline.

Two wiring quirks are load-bearing and recorded in the module doc, both
verified against a Word-produced file during research: the drawing part is
named by the data part's dsp:dataModelExt/@relId extension, and both
that id and dgm:relIds/@r:dm resolve against the host part's rels
(document or header), not the data part's own. The dsp: wrappers contain
plain a: DrawingML, so dsp:spPr parses through the existing SpPrXml,
dsp:style through ShapeStyleXml, and rendering is per-shape
build_geometry → resolve_shape_visuals → the shared shape-text
sub-layout, with labels placed in the shape's own dsp:txXfrm rectangle
(SmartArt's way of keeping text upright in rotated shapes). Nested
dsp:grpSp levels fold into their leaves at parse via §20.1.7.5's
child-space affine. A diagram without a drawing part (Word 2007 RTM,
non-Office producers) warns and draws nothing — the recorded limit.

Found in passing: the color schema expected scRgbClr, but
§20.1.2.3.30's element — and what Word actually writes, e.g. in every
dsp:style placeholder — is scrgbClr. Every real SmartArt would have
failed the whole parse on it. Fixed with the spec spelling primary and the
camel-case form kept as an alias.

Charts — drawn from the cached data

c:numCache/c:strCache are "the last data shown on the chart", and
every producer that matters writes them on save — so the renderer never
opens the embedded workbook. Drawn: 2D bar/column (clustered, stacked,
percentStacked, gapWidth/overlap incl. Word's implicit 100 for
stacks), line (blank cells break the polyline, per dispBlanksAs's
default), pie/doughnut (per-point accent colors under varyColors,
dPt overrides, firstSliceAng, holeSize, white slice separators),
area (incl. stacked), scatter (markers always, line only when the
series asks). Axes follow Excel's automatic bounds — 5% margin snapped
outward to a 1/2/5×10ᵏ unit, zero pinned unless the data floats above ⅚
of its max — plus manual min/max, maxMin reversal, c:delete
(scales the plot but isn't drawn), and majorGridlines. Legend on any
edge (categories for a one-series pie, series names otherwise), rich-text
titles and the auto series-name title. Text and chrome defaults come from
Word's own chart-style part: 9pt labels / 14pt titles, theme minor face,
#595959 text, #D9D9D9 0.75pt chrome, 2.25pt series lines, the accent1–6
cycle darkened per completed lap.

Declines are visible, not silent: radar/surface/bubble/stock warn with
their element name; 3D kinds flatten to their 2D twins at parse (the
LibreOffice reading — flattening beats refusing).

What the pipeline gained (plain shapes benefit too)

• Preset geometries beyond rect/line: roundRect, ellipse, the
  four block arrows, chevron, homePlate, diamond, triangle — the
  shapes SmartArt's layouts actually emit, from their spec guide formulas,
  with arcs as cubic Béziers and each generator's text rectangle.
• DrawingML text (a:txBody): shared schema + model, converted to
  blocks at build (where the theme can resolve scheme colors), consumed by
  SmartArt labels and chart titles alike.
• Fragment::Scene — the inline vector-scene channel. Inline drawings
  other than pictures previously rendered nothing at all; scenes now
  occupy their extent like an image and carry pre-built commands.
• Anchored scenes ride the existing floating-shape channel (empty
  geometry + scene commands), keeping text wrapping, distances and
  behind-text for free.

Tests and fixtures

• test-files/smartart.docx — a three-node process + arrow wired exactly
  as Word wires it, including the host-rels quirk. test-files/charts.docx
  — a clustered column chart (title/legend/gridlines), a varyColors pie,
  a line with a blank-cell gap and markers. Both byte-reproducible
  (scripts/make_issue155_fixtures.py) and carrying the stock Office
  theme, so accent RGBs are deterministic literals in the tests.
• tests/smartart_charts.rs (8): parse payloads; per-node accent colors
  and EMU→Pt positions; label containment and fill-under-label z-order;
  bar count and 7:4/5:4 height ratios; pie slice count/colors and its
  category legend; the polyline break and the four markers; an anchored
  chart landing at its anchor offset with wrapping intact.
• Unit tests: preset geometry tables (corner counts, adjust clamps, arrow
  tips per orientation), the diagram group-affine composition, the
  dataModelExt extraction, the chart schema (CT_Boolean's bare-element
  trap, sparse caches, 3D flattening, scatter pairing), the auto-scale
  table (zero pinning, the high-float release, the 1/2/5 ladder, manual
  bounds, percent), stacking ranges, gap runs.
• Mutation-checked: four deliberate breaks (scenes never populated,
  diagram transforms dropped, bar value scale constant, anchored arm
  severed) each fail their own tests.
• Corpus: all 28 pre-existing fixtures render byte-identical PDFs
  against main; the new fixtures verified visually (CoreGraphics
  raster) — accent-colored rounded nodes with white centered labels and
  an orange arrow; bars at the right heights with legend and gridlines,
  pie shares at 40/30/20/10, the line gap at the blank cell.

Gates

cargo fmt --check, clippy --all-targets -- -D warnings,
RUSTDOCFLAGS="-D warnings" cargo doc --no-deps,
cargo build --no-default-features and the full 45-target suite pass.
No new dependencies; public API unchanged (two new Document fields).