Spring-ai Fix: convert API records to POJOs and fix related tests

Following removal of Spring Boot's ConstructorBinding, convert record types to regular POJOs to maintain JSON serialization. Update API classes:

• Convert FunctionTool and Function records to standard Java classes with getters/setters
• Update test assertions to use getter methods instead of record accessors
• Fix failing tests in MiniMax, OpenAi and ZhiPu API implementations

This keeps core API models independent of Spring Boot while ensuring proper serialization through standard Java beans.

Comment From: markpollack

There are failing tests related to the changes. I suspect that the OPEN_AI_KEY may not have been set or the tests in spring-ai-openai weren't run before the PR was submitted. There is an issue with converting the records to classes and the calls to the openai model fail as response_format is null.

Comment From: markpollack

I'm disabling the failing tests in OpenAiResponseFormatPropertiesTests so that we can sort this out later. Look for @Disabled("GH-1645")