Propagate outages across workers

[tokebe]

Ensures outages are handled uniformly and quickly across workers, with quicker downs and quicker recoveries.

Also adds proxy scripts for outage simulation testing.

[codecov]

Codecov Report

❌ Patch coverage is 79.43262% with 29 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/retriever/utils/health_coordinator.py	75.00%	21 Missing and 2 partials ⚠️
src/retriever/background.py	0.00%	3 Missing ⚠️
src/retriever/server.py	0.00%	3 Missing ⚠️

Files with missing lines	Coverage Δ
src/retriever/config/general.py	96.26% <100.00%> (+0.02%)	⬆️
src/retriever/utils/backend_client.py	70.04% <100.00%> (+8.70%)	⬆️
src/retriever/utils/redis.py	43.93% <100.00%> (+1.90%)	⬆️
src/retriever/utils/service_health.py	63.29% <ø> (ø)
src/retriever/background.py	0.00% <0.00%> (ø)
src/retriever/server.py	0.00% <0.00%> (ø)
src/retriever/utils/health_coordinator.py	75.00% <75.00%> (ø)

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