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");