Bump version to 0.21.1 (#98)

Version bump and changelog header for the 0.21.1 release.

Add set_oblique setter and finalise oblique projection docs (#94)

Adds a set_oblique(angle, foreshortening) setter matching set_orthographic/set_perspective, and finalises the oblique projection docs with a three-panel perovskite comparison.

Bump version to 0.19.0 (#74)

Version bump and add Python 3.14 classifier.

Retire AtomData range/labels caches (closes #68)

AtomData computes global_range and global_labels eagerly in
__setitem__. The global_range() and global_labels() methods are
replaced by read-only ad.ranges and ad.labels mapping attributes
backed by MappingProxyType via @Property. Callers substitute
ad.global_range(key) with ad.ranges[key] and ad.global_labels(key)
with ad.labels[key].

AtomData.__setitem__ rejects unsupported dtypes at assignment
time with a clear ValueError. Supported dtypes are bool, integer,
float, string, and object; complex, datetime, bytes, and other
dtypes previously stored successfully but failed later in the
rendering pipeline with opaque numpy errors. _resolve_numerical
also gained a local precondition check at its values.astype(float)
site to catch any future regression in the validation chain.

resolve_atom_colours is no longer part of the public API. Colour
resolution goes through StructureScene rendering methods.

Additional correctness fixes: labels stored as immutable tuples
(previously mutable lists); empty 2-D arrays return None for
ranges instead of raising; __setitem__ computes derived metadata
into locals before mutating state.

Version bumped to 0.18.0.

Freeze AtomData entries on assignment (closes #64)

AtomData.__setitem__ now copies incoming values via numpy.array and
sets writeable=False on the stored copy. In-place mutation of a
returned array (e.g. scene.atom_data["charge"][0] = 99) raises
ValueError: assignment destination is read-only instead of silently
bypassing shape validation and cache invalidation. Callers update
values by building a new array and reassigning the key.

This is a breaking change for any code that was mutating atom_data
arrays in place, so the version is bumped to 0.17.0.

Add configurable light direction for polyhedra shading (closes #49)

New light_direction parameter on RenderStyle controls the virtual
light source for polyhedra face shading. Specified in screen space
(x=right, y=up, z=towards viewer) so users can set it in terms of
figure aesthetics ("light from the upper-left") without doing 3D
geometry in their heads.

The default changes from the viewing axis (0, 0, 1) to the upper-
left (-1, 1, 1), giving visible face brightness variation from all
viewing angles -- including top-down views of layered structures
that previously produced flat, uniform shading. The previous
behaviour can be restored with light_direction=(0, 0, 1).

Legend polyhedron icons use the same light direction as the scene
for visual consistency. render_legend() also accepts light_direction
for standalone legend rendering.

Closes #49. Bumps version to 0.16.0.

Warn when rendering species with no AtomStyle

A new _warn_missing_atom_styles helper in precompute.py emits a
single batched UserWarning per render call, listing all species in
the rendering set that lack an AtomStyle. Called once from
_precompute_scene after species resolution and before any per-atom
work, so both the radius and colour fallbacks are covered by one
upstream check.

Python's default warning filter handles deduplication: identical
messages from the same call site are shown once per process.

Bumps version to 0.15.1 since this is new user-visible behaviour
that could affect downstream CI with strict warning filters.

Per-frame colouring and validated AtomData container

Introduce per-frame colourmap-based colouring for animations and
the interactive viewer.  set_atom_data now accepts 2-D arrays of
shape (n_frames, n_atoms); the rendering pipeline slices per frame
and uses cached global ranges (numeric) and global label sets
(categorical) for consistent colour scaling across frames.
Polyhedra inherit per-frame colours from their centre atoms.

Replace the plain dict backing atom_data with a validated AtomData
container (MutableMapping) that checks array shapes on assignment.
Convert StructureScene from a dataclass to a plain class with an
explicit __init__, view property with validating setter, and
atom_data property that prevents replacement with a non-AtomData
value.  The constructor API is unchanged.

Closes #44.

v0.14.2: Fix bond completion for padding image atoms (#38)