feat: allow overriding protocol versions in Client, Server, and Transport

[mattzcarey]

Summary

Adds supportedProtocolVersions option to ProtocolOptions for custom protocol version support.

• First version in list is preferred (sent by client, fallback by server)
• Passed to transport automatically during connect()
• Inherited by both Client and Server

Usage

import { McpServer, SUPPORTED_PROTOCOL_VERSIONS } from '@modelcontextprotocol/server';

const server = new McpServer(
    { name: 'my-server', version: '1.0.0' },
    {
        supportedProtocolVersions: ['2026-01-01', ...SUPPORTED_PROTOCOL_VERSIONS]
    }
);

Test plan

• pnpm typecheck:all passes
• pnpm test:all passes

🤖 Generated with Claude Code

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Latest commit: fc89b4a

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commit: 8aaee7e