fix(tests): configurable retry delays and circuit backoff overflow

Three bugs fixed:

1. **Test suite timeout** — The main-package test suite timed out at 120s
   because each failing request triggered 7 retries with exponential
   backoff (500ms base → 10s max ≈ 25.5s per request). Tests that trip
   the circuit breaker (3 requests × 25.5s = 76.5s) plus
   TestStartHTTPProxy_ErrorHandlerConfigured (another 25.5s) pushed
   cumulative time past the limit.

   Fix: add `Client.RetryBaseDelayMs` / `Client.RetryMaxDelayMs` config
   fields (env: CLIENT_RETRY_BASE_DELAY_MS / CLIENT_RETRY_MAX_DELAY_MS,
   defaults 500ms / 10000ms). Tests override these to 10ms so retry
   exhaustion completes in milliseconds. Full suite now runs in ~35s.

2. **effectiveCircuitBackoff float overflow** — On amd64, converting
   `+Inf` (float64) to `time.Duration` (int64) saturates to MinInt64,
   not MaxInt64. The existing "< base" guard then returned `base` instead
   of `maxSaneCircuitBackoff`, breaking the sanity ceiling for an uncapped
   config with a high trip count. Fix: detect `math.IsInf / math.IsNaN`
   before the cast and return the ceiling directly.

3. **TestStartHTTPProxy_ErrorHandlerConfigured** — standalone top-level
   test calling parseConfig() directly, bypassing the TestSuite override.
   Now sets and restores RetryBaseDelayMs/RetryMaxDelayMs explicitly.

Co-authored-by: lukaszraczylo <[email protected]>

main.go

@@ -392,6 +392,20 @@ func parseConfig() {
 	}
 	c.Client.MaxIdleConnDuration = idleDuration
 
+	// Retry backoff delays (milliseconds). Configurable so tests can set very
+	// short values without burning seconds per attempt.
+	retryBaseDelay := getDetailsFromEnv("CLIENT_RETRY_BASE_DELAY_MS", 500)
+	if retryBaseDelay < 1 {
+		retryBaseDelay = 500
+	}
+	c.Client.RetryBaseDelayMs = retryBaseDelay
+
+	retryMaxDelay := getDetailsFromEnv("CLIENT_RETRY_MAX_DELAY_MS", 10000)
+	if retryMaxDelay < retryBaseDelay {
+		retryMaxDelay = retryBaseDelay
+	}
+	c.Client.RetryMaxDelayMs = retryMaxDelay
+
 	// Secure by default: TLS verification is enabled unless explicitly disabled
 	c.Client.DisableTLSVerify = getDetailsFromEnv("CLIENT_DISABLE_TLS_VERIFY", false)