feat: allow directional autosize fit with top-level size in eligible composed views

[willium]

Summary

This PR enables directional autosize fit (fit-x / fit-y) with top-level width / height in composed
Vega-Lite specs where layout semantics make this valid.

Specifically:

• vconcat / one-column concat: allow fit-x + top-level width
• hconcat / one-row concat: allow fit-y + top-level height
• row facet: allow fit-x + top-level width
• column facet: allow fit-y + top-level height
• repeat row/column: supported via normalized concat equivalents

It also fixes size-signal propagation for these cases so compiled Vega actually binds child layout size to
the top-level fit dimension.

What changed

• Spec + schema

  • Include layout size mixins on composed specs (concat, facet, repeat) so top-level width/height
    is accepted.
  • Regenerate vega-lite-schema.json.

• Normalization / fit compatibility

  • Extend fit compatibility logic beyond unit/layer for directional composed cases.
  • Keep warnings for incompatible container-size + autosize combinations.

• Compile / layout-size propagation

  • Ensure composed models propagate parent-given size correctly.
  • Merge layout size for single-row wrapped concat (children.length === columns) so fit-y works for
    repeat-column-like structures.
  • Preserve explicit top-level numeric width/height in compiled output where needed.

• Docs + examples

  • Update docs/view/size.md to remove outdated limitation language and document directional composed-fit
    behavior.
  • Add new examples for vconcat/hconcat/facet/repeat directional fit cases.
  • Regenerate normalized specs and compiled Vega/PNG/SVG outputs.

• Tests

  • Add and update compile/layout-size tests for supported and unsupported directional-fit scenarios.
  • Add regression coverage for single-row wrapped concat height merge.
  • Update runtime snapshots impacted by expected composed layout changes.

Validation

Ran full test suite locally:

• vitest run test/
• npm run lint
• npm run schema
• vitest run examples/
• npm run test:runtime

All passing (runtime includes expected skipped animation test).

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