fix(server): close stdio transport on stdin close

[harshmathurx]

Summary

• close StdioServerTransport when stdin emits close or end
• remove stdin lifecycle listeners during transport close
• add regression coverage for both stdin close paths

Fixes #2002.

Test Plan

• npx -y pnpm@10.26.1 --filter @modelcontextprotocol/server test -- packages/server/test/server/stdio.test.ts
• npx -y pnpm@10.26.1 --filter @modelcontextprotocol/server lint

[changeset-bot]

🦋 Changeset detected

Latest commit: 98f7d00

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@modelcontextprotocol/server	Patch

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commit: 98f7d00

[harshmathurx]

Pushed a small test-fixture follow-up after the Node 22 CI failure.

The failing job crashed because serverThatHangs.ts can receive SIGTERM after the stdio transport has already closed, then its late sendLoggingMessage() rejection escapes the signal handler. The fixture now ignores that expected late logging failure so the test keeps exercising process cleanup instead of crashing during teardown.

Local verification:

• corepack pnpm --dir test/integration test -- processCleanup.test.ts (ran the integration suite; 18 files / 353 tests passed)
• git diff --check