types: Setting default value for jsonrpc

[sreenaths]

The JSON-RPC version is fixed at 2.0 for MCP messages. However, as the value is not set by default, we have to pass the correct value every time a model is instantiated.

Motivation and Context

This change simplifies model instantiation by automatically setting the JSON-RPC version. Additionally, if the version ever needs to change in the future, it only has to be updated in a single place.

For example

JSONRPCMessage(
    root=JSONRPCRequest(
        # jsonrpc="2.0", - This wouldn't be required
        id=1,
        method="ping"
    )
),

How Has This Been Tested?

Tests were improved and are working as expected.

Breaking Changes

No

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

None

[sreenaths]

Hi @ochafik
When you have a chance, please review this PR.
It is similar to PR #1292 that you had helped with before.
Thank you.