Performance and other improvements

[jpodivin]

Upon examination, it turned out that we are mostly right about the worker number. In fact, even 4 may be an overkill, since we are I/O bound. I have at least parametrized it, so we can adjust the value in production.

Further changes:

• Timestamps are now handled more consistently, as a datetime object until use
• Http client is initialized once
• Tasks are tracked and their state verified upon exit
• Server has a lifespan manager, disposing of tasks gracefully
• The logger initialization has been normalized
• We are now mocking the LD_URL in tests

[gemini-code-assist]

Code Review

This pull request introduces a global AsyncClient for HTTP requests and implements a lifespan manager to ensure background tasks are completed during application shutdown. It also refactors the handling of analysis start times to use datetime objects instead of strings and improves task error reporting via Sentry. A review comment suggests explicitly closing the http_client within the lifespan manager to ensure all resources are properly released.

[Jany26]

I wonder if we should add some config file, as the number of env variables keeps increasing 😅