[chore] Prepare for v9.1 publish

[ibgreen-openai]

• Unwind beta versions to 9.1.0.
• Move some unused code.

[Copilot]

Pull Request Overview

This PR prepares the project for the 9.1.0 release by unwinding beta versions, updating dependencies across modules and examples, bumping the Yarn package manager version, and removing obsolete config from examples.

• Bump module and example package versions from beta to stable 9.1.0
• Update Yarn packageManager to 4.9.0 in root and website
• Remove unused Volta config in examples and clean up deprecated README

Reviewed Changes

Copilot reviewed 32 out of 67 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
website/package.json	Bumped Deck.GL deps to 9.1.0 and added packageManager
package.json	Updated Yarn packageManager to 4.9.0
modules/react/package.json	Bump version to 9.1.0
modules/leaflet/package.json	Bump version to 9.1.0
modules/layers/package.json	Bump version to 9.1.0
modules/infovis-layers/package.json	Bump version to 9.1.0
modules/graph-layers/package.json	Bump version to 9.1.0
modules/geo-layers/package.json	Bump version to 9.1.0
modules/experimental/package.json	Bump version to 9.1.0
modules/editable-layers/package.json	Bump version to 9.1.0
modules/bing-maps/package.json	Bump version to 9.1.0
modules/arrow-layers/package.json	Bump version to 9.1.0
lerna.json	Update monorepo version to 9.1.0
examples/infovis-layers/horizon-graph-layer/package.json	Bump example deps to ^9.1.0
examples/graph-layers/graph-viewer/package.json	Bump example deps to stable 9.1.0
examples/graph-layers/graph-viewer-legacy/package.json	Bump deps, remove Volta config
examples/editable-layers/sf/package.json	Bump example deps to ^9.1.0
examples/editable-layers/editor/package.json	Bump example deps to ^9.1.0
examples/editable-layers/editable-h3-cluster-layer/package.json	Bump example deps to ^9.1.0
examples/editable-layers/advanced/package.json	Bump example deps to ^9.1.0
examples-wip/playground/package.json	Bump deps and constants to ^9.1.0
examples-wip/codesandbox/world-heritage/package.json	Bump @deck.gl-community/react to ^9.1.0
examples-wip/arrow-layers/trips/package.json	Remove Volta config
examples-wip/arrow-layers/text/package.json	Remove Volta config
examples-wip/arrow-layers/polygon/package.json	Remove Volta config
examples-wip/arrow-layers/point/package.json	Remove Volta config
examples-wip/arrow-layers/multipolygon/package.json	Remove Volta config
examples-wip/arrow-layers/multipoint/package.json	Remove Volta config
examples-wip/arrow-layers/multilinestring/package.json	Remove Volta config
examples-wip/arrow-layers/linestring/package.json	Remove Volta config
docs/modules/experimental/README.md	Update experimental module version heading
deprecated/README.md	Remove old deprecated content

Comments suppressed due to low confidence (2)

docs/modules/experimental/README.md:28

• Update the experimental module version heading to v9.1.0 to match the module version bump.

### `@deck.gl-community/experimental` v9.0.0