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

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🦋 Changeset detected

Latest commit: 2656e1f

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: 2656e1f