feat: add matryoshka embedding truncation

[Bbbtt04]

Summary

• Add an optional Document Store embedding setting to keep only the first N embedding dimensions for Matryoshka-compatible models.
• Apply truncation consistently for document indexing and retrieval query embeddings.
• Keep the provider init inputs clean while recording the truncation setting in upsert history.

Closes #4361

Tests

• pnpm --filter flowise-components exec jest src/matryoshkaEmbeddings.test.ts --runInBand
• pnpm --filter flowise-components exec tsc --noEmit --pretty false
• pnpm --filter flowise-components exec eslint src/matryoshkaEmbeddings.ts src/matryoshkaEmbeddings.test.ts nodes/vectorstores/DocumentStoreVS/DocStoreVector.ts --ext ts --max-warnings 0
• pnpm exec eslint packages/server/src/services/documentstore/index.ts packages/ui/src/views/docstore/VectorStoreConfigure.jsx --ext ts,jsx --max-warnings 0
• pnpm --filter flowise-components build
• pnpm --filter './packages/server' exec tsc --noEmit --pretty false
• pnpm --filter flowise-ui build

[gemini-code-assist]

Code Review

This pull request introduces Matryoshka embedding truncation support, allowing users to optionally truncate document and query embeddings to a configured dimension. It adds a utility module matryoshkaEmbeddings.ts along with unit tests, integrates this truncation into the document store services, and updates the UI to support configuring the truncation dimensions. The review feedback highlights a potential runtime crash when using Object.create on embedding instances that utilize native JavaScript private fields, suggesting a monkey-patching approach instead. Additionally, it recommends using loose equality (== null) for nullish checks in accordance with standard idioms.

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[gemini-code-assist]

Using Object.create(embeddings) to wrap the embeddings instance can cause runtime crashes if the underlying class uses native JavaScript private fields (e.g., #apiKey). Any non-overridden method called on the prototype-derived wrappedEmbeddings object that accesses these private fields will throw a TypeError: Cannot read private member from an object whose class did not declare it.

Since the embedding instance is created fresh for each operation and is not shared globally, directly monkey-patching the methods on the original embeddings instance is a much safer and robust approach that preserves the this context and private field access.

    const originalEmbedDocuments = embeddings.embedDocuments.bind(embeddings)
    const originalEmbedQuery = embeddings.embedQuery.bind(embeddings)

    embeddings.embedDocuments = async (documents: string[]): Promise<number[][]> => {
        const vectors = await originalEmbedDocuments(documents)
        return vectors.map((vector) => truncateVector(vector, dimension))
    }

    embeddings.embedQuery = async (document: string): Promise<number[]> => {
        const vector = await originalEmbedQuery(document)
        return truncateVector(vector, dimension)
    }

    return embeddings

[gemini-code-assist]

According to the general rules, loose equality (== null) should be used as a standard idiom for a 'nullish' check that covers both null and undefined.

Suggested change

	if (value === undefined || value === null || value === '') return undefined
	if (value == null || value === '') return undefined

References

1. In JavaScript/TypeScript, use loose equality (== null) as a standard idiom for a 'nullish' check that covers both 'null' and 'undefined'.