…rix types, and dispatch API

Adds a new coordinax._src.metric package with four modules: field.py (AbstractMetricField, AbstractDiagonalMetricField, RoundMetric), matrix.py (AbstractMetricMatrix, DiagonalMetric, DenseMetric), api.py (metric_matrix, metric_representation fallback dispatches), and __init__.py. AbstractMetric/AbstractDiagonalMetric in base/metric.py are renamed to AbstractMetricField/AbstractDiagonalMetricField and stripped of their metric_matrix method — that computation is now a standalone dispatch function.

…e_factors, and rename metric classes

Each geometry (Euclidean, HyperSpherical, Minkowski, Product, Embedded, Custom) gains a register_metric.py module that registers metric_matrix and metric_representation dispatches using the new standalone dispatch API. Metric class names are updated: EuclideanMetric → FlatMetric, HyperSphericalMetric → RoundMetric, CartesianProductMetric → ProductMetric, InducedMetric → PullbackMetric. Spherical and Minkowski geometries receive new scale_factors.py files. The metric_matrix method is removed from each metric class in favour of the dispatch function.

…ic symbols

The coordinax.api.manifolds dispatch API gains metric_matrix and metric_representation. The coordinax.manifolds re-export module is updated to expose the renamed metric classes (FlatMetric, RoundMetric, ProductMetric, PullbackMetric) and new matrix types (AbstractMetricMatrix, DiagonalMetric, DenseMetric). AbstractManifold is updated to use AbstractMetricField. The scale_factors dispatch file gains metric-aware overloads. Public internal.py and main.py re-exports are aligned with the new names.

…, representations, transforms, vectors, distances, and frames

All references to QuantityMatrix (now QMatrix), EuclideanMetric (now FlatMetric), HyperSphericalMetric (now RoundMetric), CartesianProductMetric (now ProductMetric), InducedMetric (now PullbackMetric), AbstractMetric (now AbstractMetricField), and AbstractDiagonalMetric (now AbstractDiagonalMetricField) are updated throughout the core modules and their tests. Docstring Examples section headers that merely introduce the code block are also removed for cleaner inline doctests.

…ng cleanup

Remove Examples section headers from docstrings in distance_modulus, frame_transforms, parallax, register_constructors, and register_converters. Update tests to use new metric and frame API conventions.

…ld API

Remove unused register_frames dispatches and update tests to match the current frame and manifold API conventions.

…anifold API

Update strategy tests and chart/vector/distance tests to reflect the current API conventions introduced by the metric refactor.

…ocstring cleanup

Replace QuantityMatrix with QMatrix in qmatrix.py and remove Examples section headers from angles, distances, frames, ptmap, vec_constructors, and vec_converters. Tests updated to match.

spec.md is updated to reflect the new metric module design (AbstractMetricField, metric_matrix dispatch, DiagonalMetric/DenseMetric matrix types). API and guide pages for manifolds, charts, and representations are updated to use the new class names. README and tutorials are adjusted for minor API changes.

Add jax.extend.core and jax.tree_util import abbreviations to pyproject.toml. Add ARG002 (unused method argument) to per-file test ignores to allow pytest fixture parameters that are injected but not referenced in the body.

Replace float literals (1.0, 2.0, etc.) with integer literals where values are whole numbers, and normalize rtol=0.0 to rtol=0 in assert_allclose calls.

…ity_matrix tests

Replace float literals like 1.0, 2.0 with int equivalents where the values are whole numbers. Preserve floats where needed for JAX grad/jvp tests, dtype-sensitive operations, and mixed-unit conversion tests that produce float results.