implement router for handling requests

[kbarbounakis]

This pull request closes #85 and introduces batch request support to the application, allowing multiple API calls to be executed in a single HTTP request. It also adds corresponding tests and updates dependencies. The most significant changes are the implementation of the batch processing middleware, the addition of comprehensive tests for batch functionality, and dependency updates.

Batch request support:

• Added a new batch middleware in src/batch.js that processes batch API requests, handling each sub-request with its own request and response objects and returning aggregated results.
• Exported the new batch middleware from src/index.js for use in other modules.

Testing:

• Added a new test suite in spec/batch.spec.js to verify batch request handling, including scenarios for successful batch execution and handling of non-existing endpoints.

Dependency updates:

• Updated @themost/data to version 2.23.2 and downgraded @themost/sqlite to 2.11.1 in package.json to ensure compatibility.

Test configuration:

• Increased the Jest test timeout from 15 seconds to 45 seconds in jest.setup.js to accommodate longer-running batch tests.