fix: nullable json-rpc id instead of optional

[Liooo]

Deny undefined for json-rpc error response id, make it spec compliant.

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

id
This member is REQUIRED.
It MUST be the same as the value of the id member in the Request Object.
If there was an error in detecting the id in the Request object (e.g. Parse error/Invalid Request), it MUST be Null.

Fix for the change in: #1242.
Related: modelcontextprotocol/modelcontextprotocol#1939

How Has This Been Tested?

unit tests, type checking

Breaking Changes

undefined won't be allowed as id

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

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/sdk@1281 

commit: df0dc31