feat: add the resource replacement controller and schema contract

[Maxxich]

Depends on PR: refactor: share lazily initialized editor dependencies.

Define opt-in NodeSpec._resource metadata and a shared asynchronous controller.
Deduplicate requests by kind/value, validate responses, handle cancellation and
timeouts, and expose engine-independent resource reading and replacement helpers.
URL normalization remains separate from opaque identifiers. Include unit coverage
with the core behavior; editor adapters are connected in dependent changes.

Summary by Sourcery

Introduce the shared resource replacement contract and controller, while enabling reusable lazy editor dependency preparation.

New Features:

• Add opt-in resource metadata and shared helpers for reading, validating, and replacing node resources across editor modes.
• Add an asynchronous resource replacement controller with request deduplication, cancellation, timeouts, response validation, lifecycle events, and error handling.

Enhancements:

• Separate URL normalization and validation from opaque resource identifiers while excluding code content from replacements.
• Support lazily prepared and reusable editor dependencies without accumulating editor-specific plugins or components.

Tests:

• Add unit coverage for resource replacement lifecycle behavior, schema validation, URL handling, opaque identifiers, and shared editor dependency reuse.

[gravity-ui]

[gravity-ui]

[sourcery-ai]

Hey - I've reviewed your changes and they look great!

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