fix McpSchema deserialization issues with Jackson3 while keeping Jackson2 behavior unchanged

[iuliiasobolevska]

Motivation and Context

Fixes #978

How Has This Been Tested?

Added unit tests utilizing both Jackson2 and Jackson3

Breaking Changes

I spent several cycles trying to find a solution that keeps behavior unchanged when Jackson2 is being used while fixing the deserialization issue for Jackson3:

• Jackson 2: picks fromJson as before
• Jackson 3: with @JsonCreator(mode = JsonCreator.Mode.DISABLED) on the canonical constructor, Jackson 3 no longer treats it as a candidate creator. It then falls back to the @JsonCreator-annotated static fromJson factory — the same creator used by Jackson 2. Both mappers now route deserialization through fromJson.
• Programmatic Java with null: still throws IllegalArgumentException as before (backward compatible).

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