fix: make in-memory event replay use stored stream ids

[Genmin]

Summary

• Look up the stream id from the stored event metadata instead of parsing the generated event id.
• Replay events in insertion order so events stored in the same millisecond are not reordered by the random id suffix.
• Add regression coverage for the standalone SSE stream id used by GET streams.

Fixes #943

Tests

• pnpm --filter @modelcontextprotocol/test-integration exec vitest run test/taskResumability.test.ts
• pnpm --filter @modelcontextprotocol/examples-server run typecheck
• pnpm --filter @modelcontextprotocol/examples-server run lint
• pnpm --filter @modelcontextprotocol/test-integration run lint
• Pre-push hook: full lint, build, and typecheck suite passed

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Latest commit: 17fb9ec

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commit: 17fb9ec