chore: Spring 5 compatibility

[He-Pin]

Motivation and Context

#648

How Has This Been Tested?

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[He-Pin]

@tzolov wdyt about this, otherwise, we have to do a fork:(

[Kehrlann]

I'm ok with this in principle, but the tests don't pass.

[He-Pin]

let't me check this, thanks.

[He-Pin]

@Kehrlann I just run the test locally, it pass.
WebFluxStreamableIntegrationTests.testRootsWithMultipleHandlers

And the fails

Error has been observed at the following site(s):
	*__checkpoint ⇢ 503 SERVICE_UNAVAILABLE from DELETE http://localhost:52887/otherPath/mcp/message [DefaultWebClient]
``` should be a bug in the test suite, where, I think we should call `DELETE` on `http://localhost:52887/otherPath/mcp/` but not `http://localhost:52887/otherPath/mcp/message `

[He-Pin]

@Kehrlann Thank you very much for this.