refactor: SentryReporter enabled guard, per-instance unmatched-secondary buffer, deterministic tests

[Copilot]

Four review fixes for the redis-proxy shadow pub/sub and Sentry reporter.

Changes

• SentryReporter.ShouldReport enabled guard (sentry.go): Add early return false when disabled, eliminating mutex acquisition and map churn on every secondary write when Sentry is not configured. Add injectable nowFunc to the struct.

• Per-instance unmatchedSecondaries (shadow_pubsub.go): Remove the package-level global sync.Mutex + map[*shadowPubSub]map[...] that serialized buffering/sweeping across all instances. Replaced with a map[msgKey][]secondaryPending field on shadowPubSub itself, protected by the existing sp.mu. Simplifies locking in matchSecondary, reconcileWithBufferedSecondary, sweepExpired, sweepAll, and Close.

• Remove //nolint:exhaustive (shadow_pubsub.go): Replace the two-branch switch in reportDivergence with an explicit if d.kind == DivExtraData so future DivergenceKind additions are caught at compile/lint time rather than silently falling to a default.

• Deterministic Sentry cooldown tests (proxy_test.go): TestShouldReportCooldown and TestShouldReportEvictsExpired previously used time.Sleep to wait out cooldown windows. Both now manipulate the injected nowFunc directly:

now := time.Now()
r := &SentryReporter{
    enabled:  true,
    cooldown: 50 * time.Millisecond,
    nowFunc:  func() time.Time { return now },
    ...
}
assert.True(t, r.ShouldReport("fp1"))
assert.False(t, r.ShouldReport("fp1"))   // still within cooldown
now = now.Add(60 * time.Millisecond)      // advance clock, no sleep
assert.True(t, r.ShouldReport("fp1"))    // cooldown elapsed

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[bootjp]

@copilot fix golangci-lint

[Copilot]

@copilot fix golangci-lint

Fixed in 28c1d9b. The gci formatter required double-space alignment before the inline comment on line 311 of proxy_test.go (now = now.Add(60 * time.Millisecond) // advance past cooldown).