Fix JSON-RPC notification format in Streamable HTTP transport

[dak2]

Motivation and Context

Update send_notification method to properly construct JSON-RPC notification objects with jsonrpc version and method fields.
This ensures notifications conform to the JSON-RPC 2.0 specification when sent over HTTP transport.

https://www.jsonrpc.org/specification#notification

Another goal is to standardise the send_notification interface.
Before the revision, it was sufficient to pass the method and parameters in the case of stdio.
However, in the case of Streamable, a hash based on the JSON-RPC specification must be passed.

How Has This Been Tested?

It is covered by existing tests for this case.

Breaking Changes

There's a potential impact on clients receiving notifications, because this modification will structure them.

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