Refactor ProcessRequest for Anthropic messages interception

[ssncferreira]

Description

The messages package has the most duplication between its blocking and streaming ProcessRequest implementations.

Tasks:

• Identify the flow that ProcessRequest follows in both blocking and streaming
• Extract the tool result content conversion (TextContent, EmbeddedResource, BlobResourceContents handling) into a shared method on interceptionBase
• Extract tool call handling and recording logic as methods on interceptionBase, following the pattern already established in the responses package
• Fix bugs found during the refactor
• Add unit tests for the extracted methods