Default Environment should be appended with custom env's passed to client (instead of replacing)

[Pdash-exceeds]

Describe the bug
In this line

typescript-sdk/src/client/stdio.ts

Line 119 in 0fa2397

env: this._serverParams.env ?? getDefaultEnvironment(),

To Reproduce
Steps to reproduce the behavior:

1. Connect a stdio client without custom env (works)
2. Connect the same client with custom env (fails because HOME, PATH and other default envs are missing when spawning the process)

Expected behavior
Both cases should pass.
env: { ...getDefaultEnvironment(), ...(this._serverParams.env ?? {}) },

Logs
file:///Users/pradeeptadash/langchain_mcp/node_modules/@langchain/mcp-adapters/dist/src/client.js:407
throw new MCPClientError(Failed to connect to stdio server "${serverName}": ${error}, serverName);
^

MCPClientError: Failed to connect to stdio server "linear-server": Error: spawn npx ENOENT
at MultiServerMCPClient.initializeStdioConnection (file:///Users/pradeeptadash/langchain_mcp/node_modules/@langchain/mcp-adapters/dist/src/client.js:407:19)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async MultiServerMCPClient.initializeConnections (file:///Users/pradeeptadash/langchain_mcp/node_modules/@langchain/mcp-adapters/dist/src/client.js:371:17)

Additional context
Add any other context about the problem here.