Extension to #851 and #511

Motivation and Context

The SDK currently exports from all files, which leads to users/implementors having to import from multiple places from the SDK.

Example:

import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { isInitializeRequest, LoggingLevelSchema, SetLevelRequestSchema } from '@modelcontextprotocol/sdk/types.js';

This PR introduced index.ts barrel files under the following namespaces:

• @modelcontextprotocol/sdk/server
• @modelcontextprotocol/sdk/client
• @modelcontextprotocol/sdk/shared (a new export added to package.json)

The above snippet would now look like:

import { StreamableHTTPServerTransport, McpServer } from '@modelcontextprotocol/sdk/server';
import { isInitializeRequest, LoggingLevelSchema, SetLevelRequestSchema } from '@modelcontextprotocol/sdk/shared';

How Has This Been Tested?

Unit tests continue to run with no issues.

Breaking Changes

No, it's an improvement and not a breaking change.

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

There are two files which were a bit controversial "./types.ts", and "./inMemory.ts". These are currently residing at the root level, although they are really "shared". Thus the shared namespace is re-exporting them.

Additionally, the previous client/index.ts contents was moved to client/client.ts and server/index.ts was moved to server/server.ts respectively. Since these two files are now re-exported by the index.ts files, there is no breaking change.