BE: Handle Flux response bodies in MCP tool call results

[elvis-cai]

• Breaking change? (if so, please describe the impact and migration path for existing application instances)

What changes did you make? (Give an overview)
Problem:
When MCP tools return Mono<ResponseEntity<Flux<?>>>, the response body contains a Flux stream that wasn't being properly handled, which
could cause issues when trying to serialize the result for the MCP client.

Solution:
Modified the reponseToCallResult method to detect when the ResponseEntity body is a Flux and automatically collect it into a list before
converting to CallToolResult. This ensures streaming responses are properly materialized before being serialized.

Changes:

• In McpSpecificationGenerator.java:93-101, added a check for Flux<?> response bodies
• When detected, the Flux is collected via flux.collectList().map(this::callToolResult)
• Non-Flux responses continue to work as before

This allows MCP tools to return streaming responses (Flux) wrapped in ResponseEntity while ensuring they're properly handled and sent
back to the MCP client as serialized lists.
fix (#1454)
Is there anything you'd like reviewers to focus on?

How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

• No need to
• [] Manually (please, describe, if necessary)
• [] Unit checks
• [] Integration checks
• Covered by existing automation

Checklist (put an "x" (case-sensitive!) next to all the items, otherwise the build will fail)

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g. ENVIRONMENT VARIABLES)
• My changes generate no new warnings (e.g. Sonar is happy)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

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[github-actions]

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[germanosin]

Thanks for contribution. Please check my comment

[germanosin]

I would prefer to see this trick in the callToolResult method

[elvis-cai]

thanks for the quick review, good point, updated