[Bug]: Pipelines not working on Python 3.9 and 3.10

[r4victor]

Steps to reproduce

1. Run dstack server on Python 3.9 and 3.10.
2. Try submitting any resource and see it being stuck in submitted/pending.

Actual behaviour

The module-level instantiation _pipeline_manager = PipelineManager() creates asyncio primitives outside of a running event loop on Python 3.9 and 3.10. On Python 3.11+ these primitives no longer bind to a loop in __init__() — they lazily get the running loop when first used, so the module-level instantiation works fine. PipelineManager() should not be done at the module level but initialized lazily.

Update: The real root cause is that on Python before 3.11, timeout error is asyncio.Timeout but we were handling only TimeoutError:

dstack/src/dstack/_internal/server/background/pipeline_tasks/base.py

Lines 298 to 303 in c0c011c

	await asyncio.wait_for(
	self._fetch_event.wait(),
	timeout=self._next_fetch_delay(empty_fetch_count),
	)
	except TimeoutError:
	pass

Still a good idea to move pipeline manager init out of module init.

Expected behaviour

No response

dstack version

master

Server logs

Additional information

No response