fix(redis): make Sentinel clients resilient to dropped connections

[etiennecrb]

Redis backends built via redis_client()/async_redis_client() opened Sentinel connections with no health check and no retry, so a transient connection reset (Connection reset by peer on the Sentinel port) surfaced as MasterNotFoundError even though a healthy master existed.

Set health_check_interval, socket_keepalive and a retry on ConnectionError/ TimeoutError on both the Sentinel-node and master connections, for the sync and async clients and the plain (non-Sentinel) URL path. MasterNotFoundError is a ConnectionError, so discovery blips are now retried transparently. Applied unconditionally so the scheduler client (built without socket_timeout) is covered too.

[Copilot]

Pull request overview

This PR improves the robustness of Redis client creation in Remoulade by configuring health checks and automatic retries for both Sentinel-based and direct Redis URL connections, across sync and async clients. This prevents transient connection resets (including Sentinel master discovery blips) from surfacing as persistent failures.

Changes:

• Introduces shared connection defaults (health checks, TCP keepalive, and retry policy) via a helper in redis_client.py.
• Applies the same resiliency parameters to Sentinel node connections and master connections for both sync and async Redis clients.
• Adds tests asserting these connection parameters are set for Sentinel URLs, plain Redis URLs, and the no-socket_timeout scheduler-style configuration.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
remoulade/helpers/redis_client.py	Centralizes and applies Redis connection resiliency defaults (health checks + retries) for sync/async and Sentinel/plain URL paths.
tests/test_helpers.py	Adds unit tests validating resilient connection kwargs are configured on created Redis clients.

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