- Add retry_count to HookTask with serde(default) for backwards compat
- Limit hook task retries to MAX_RETRIES=5, discard after limit to prevent
infinite requeue loops that caused 'task nack'd and requeued' log spam
- Add nak_with_retry() in RedisConsumer to requeue with incremented count
- Standardize all slog logs: replace "info!(l, "msg"; "k" => v)" shorthand
with "info!(l, "{}", format!("msg k={}", v))" across ssh/authz.rs,
ssh/handle.rs, ssh/server.rs, hook/webhook_dispatch.rs, hook/pool/mod.rs
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