Release v0.9.0

Summary

Minor release that pulls in upstream oxidize-pdf v2.14.0 and exposes its new
gradient-rendering capability in the Python bridge.

Upstream 2.14.0 makes axial and radial shadings actually render: a shading
now emits a real PDF /Function (Type 2 exponential for two colour stops, Type
3 stitching for more) together with the required /ColorSpace, instead of the
previous placeholder /Function 1 integer with no paint operator (upstream
#297). The bridge already exposed the shading definition types
(AxialShading, RadialShading, ShadingManager), but they were a dead end:
there was no way to attach a shading to a page nor to paint it. This release
adds the missing paint path.

This is a non-breaking, additive change at the API level. Every previously
callable method preserves its signature; the new methods are purely additive.
The text-extraction quality fixes from upstream (word scramble in dense and
multi-column documents #302/#305, the chunk_text infinite-loop guard #308, and
the non-ASCII WinAnsi glyph measurement corrections #309/#313) are inherited
transparently through the version bump with no bridge API change.

Upstream

• oxidize-pdf =2.13.0 → =2.14.0. Pinned exact equality preserved; the
  feature set is unchanged (compression, signatures, semantic, language-detection, default-features = false).
• Upstream 2.14.0 added real gradient rendering (#297) and fixed: word scramble
  from unresolved indirect /Font dictionaries and overlapping font-switched
  runs (#302, #305), a DocumentChunker::chunk_text infinite loop (#308), and
  measure_text/get_string_width over-measuring non-ASCII WinAnsi glyphs
  (#309, #313).

Added

Gradient rendering (Page)

The canonical bounded-gradient idiom is: register a shading, then bound it with
a clip and paint it —
add_shading → save_graphics_state → build a path → clip → end_path →
paint_shading → restore_graphics_state (the PDF q … W n /Sh sh … Q
sequence).

• Page.add_shading(name, shading) — registers an AxialShading or
  RadialShading under /Resources/Shading/<name>. name must be a valid PDF
  resource name; an invalid name raises PdfError and a non-shading object
  raises TypeError.
• Page.paint_shading(name) — emits the sh operator, painting the named
  shading into the current clip region. If name was never registered the
  operator is still emitted but references an undefined resource (no /Shading
  dict is written); conforming viewers skip the paint.
• Page.clip() / Page.clip_even_odd() — emit the W / W* clip-path
  operators, intersecting the clipping region with the current path using the
  non-zero winding or even-odd rule. Bound an arbitrary-shaped gradient region.
• Page.end_path() — emits the n operator, terminating a clip path
  (W n / W* n) without filling or stroking.

Rectangular gradient regions can also be bounded with the existing
Page.set_clipping_path; the new clip / end_path pair covers
arbitrary-shaped clips.

Compatibility

Fully backward compatible. All 2038 pre-existing tests pass unchanged; 12 new
tests cover the added surface: exact content-stream operators in document order
(W → n → /Sh sh), resource registration (/ShadingType 2 axial,
/ShadingType 3 radial), a real /FunctionType 2 exponential function for a
two-stop axial gradient (the #297 proof), two shadings coexisting on one page,
the unregistered-name contract, and the invalid-name / non-shading-object error
paths. mypy and cargo clippy -D warnings are clean; the full suite is 2050
passing.