feat(joint-react): paper provider

[samuelgja]

feat(joint-react): introduce PaperProvider and unify Paper context handling

🔗 https://github.com/orgs/clientIO/projects/6/views/13?pane=issue&itemId=112378942

Description

This PR introduces a new <PaperProvider> component and refactors how the Paper component interacts with context. This provides more flexible, explicit control over the paper instance in complex React applications.

Changes

• New component: PaperProvider for managing shared paper context
• Refactored Paper to consume existing context from PaperProvider, or fallback to self-managed context
• Context-aware behavior: Paper now reuses the nearest <PaperProvider> in the tree
• Added dev-mode warning:
  When using PaperProvider, any paper options passed directly to <Paper /> are ignored — a console warning will now inform the developer of this to prevent confusion
• Improved type safety and clarity in PaperContext, hooks, and providers
• New tests: Validate shared context behavior and paper option propagation
• Docs and README updated with examples

Usage of PaperProvider

<PaperProvider width={800} height={600}>
  <Paper renderElement={renderFn} />
</PaperProvider>