feat: add REDIS_OP_TIMEOUT for per-operation Redis timeout

[hoangcn95]

Description

REDIS_TIMEOUT only bounds the dial. Once connected, radix v4 has no read/write timeout — a command is bounded only by the caller's context, and the hot rate-limit path passes the inbound gRPC context, which usually carries no deadline. When Redis stalls, calls park indefinitely, goroutines pile up, and the pod OOMs.

This PR adds two new settings, REDIS_OP_TIMEOUT and REDIS_PERSECOND_OP_TIMEOUT, both disabled by default. When enabled, each Redis command or pipeline gets its context wrapped with a deadline, bounding per-operation latency independent of the caller's context.

Variable	Description	Default
REDIS_OP_TIMEOUT	Bounds a single Redis command or pipeline using context.WithTimeout. Set to 0 to disable.	0
REDIS_PERSECOND_OP_TIMEOUT	Same, for the per-second pool.	0

Architecture

flowchart LR
    A[gRPC request] --> B[DoLimit]
    B --> C[PipeDo / DoCmd]
    C --> D{opTimeout > 0?}
    D -->|yes| E[context.WithTimeout deadline]
    D -->|no| F[caller ctx, no deadline]
    E --> G[radix client]
    F --> G
    G --> H[(Redis)]

    style E fill:#2a9d5c,color:#fff
    style C fill:#2563eb,color:#fff

Loading

Legend: 🟢 new — 🔵 rewired

Test Result

Added unit tests in src/redis/driver_impl_test.go using the existing recordingRedisClient / testAction fakes (whitebox tests already in that package):

• TestPipeDoReturnsWithinOpTimeoutWhenRedisHangs / TestDoCmdReturnsWithinOpTimeoutWhenRedisHangs: simulate a Redis that never responds (blockDelay: time.Hour) and assert that with opTimeout = 30ms, both PipeDo and DoCmd return a context.DeadlineExceeded error in well under 500ms instead of blocking indefinitely.
• TestPipeDoAppliesOpTimeoutDeadlineToContext / TestDoCmdAppliesOpTimeoutDeadlineToContext: assert the context handed to the underlying radix client carries a deadline when opTimeout > 0.
• TestPipeDoWithoutOpTimeoutLeavesContextUnbounded / TestDoCmdWithoutOpTimeoutLeavesContextUnbounded: assert no deadline is added when opTimeout == 0, preserving current behavior exactly.

Settings parsing is covered in src/settings/settings_test.go (TestRedisOpTimeout_Default, TestRedisOpTimeout_Configured), mirroring the style of the settings tests added in #1018.

All of the above pass under go test -race, along with the full existing suite (./...).

Load test

• TBD