Add unit tests and type definitions for Diffbot knowledge connectors

[Copilot]

Adds unit test coverage and TypeScript type definitions for the Diffbot webcrawler and webpage knowledge connectors, which previously had none.

Type definitions (types.ts)

• Crawler API types: CrawlJobSettings, DiffbotResult, DiffbotJobStatus, DiffbotCrawlJob, DiffbotCreateCrawlResponse, DiffbotJobStatusResponse
• Webpage API types: DiffbotArticle, DiffbotV3AnalyzeResponse, DiffbotRequest, DiffbotImage, DiffbotTag, DiffbotBreadcrumb, DiffbotCategory

Unit tests — diffbotCrawlerConnector

• Source creation with chunks from crawled pages
• Multi-page crawl producing multiple sources
• Upsert of existing source with content hash change
• Stale source deletion when crawl returns different pages
• Skips chunk ingestion when upsertKnowledgeSource returns null (content unchanged)
• retainCrawler: true suppresses job deletion
• Pages missing pageUrl are skipped
• Query string passthrough

Unit tests — diffbotWebpageConnector

• Source creation with chunks
• Multi-object response produces one source per object with indexed externalIdentifier
• Upsert of existing source
• Stale source deletion
• Skips chunks when upsert returns null
• Throws when Diffbot returns empty objects array

All tests use Node.js built-in node:test + mock.fn/mock.method, consistent with the rest of the repo.

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[graymalkin77]

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