feat(controlplane): run federated graph composition in worker pool to unblock main event loop

[pepol]

• feat(controlplane): run federated composition in worker pool to unblock main event loop

Summary by CodeRabbit

• New Features

  • Composition now runs on a dedicated worker pool, improving concurrency and reliability for graph creation, updates, moves, subgraph operations, monograph/contract flows, and feature-flag workflows.

• Chores

  • Added configurable composeWorkers (maxCount) and integrated worker-pool lifecycle into server startup and graceful shutdown.

• Tests

  • Test setup exposes the new compose worker pool for integration testing.

Checklist

• [ ] I have discussed my proposed changes in an issue and have received approval to proceed.
• [ ] I have followed the coding standards of the project.
• [ ] Tests or benchmarks have been added or updated.
• [ ] Documentation has been updated on https://github.com/wundergraph/cosmo-docs.
• [ ] I have read the Contributors Guide.