Spring AI AzureVectorStore throws UnsupportedOperationException when performing similarity search due to immutable metadata map

Bug Description

The AzureVectorStore throws an UnsupportedOperationException when performing similarity searches. The error occurs because the code attempts to modify an immutable metadata map during result processing.

Environment

• Spring AI version: 1.0.1
• Java version: 21

Steps to Reproduce

1. Configure AzureVectorStore with Azure AI Search backend
2. Index documents using Azure AI Search indexer with skillset (document chunking and embedding generation)
3. Perform a similarity search using Spring AI's VectorStore interface: ```java List results = vectorStore.similaritySearch("your query here");

Comment From: jinlee1703

I can reproduce this when the Azure result metadata map is immutable. The mapping logic later injects distance into the metadata and triggers UnsupportedOperationException. I’ll submit a PR to defensively copy incoming metadata into a mutable map before building the Document (and then set DocumentMetadata.DISTANCE). This mirrors the defensive fixes we’ve applied in other stores.

Comment From: injae-kim

Fix PR: https://github.com/spring-projects/spring-ai/pull/4131 PTAL :)