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]>

struct_config.go

@@ -42,19 +42,21 @@ type config struct {
 		PerUserCacheDisabled  bool // Disable per-user cache isolation (SECURITY RISK - not recommended)
 	}
 	Client struct {
-		GQLClient           *graphql.BaseClient
-		FastProxyClient     *fasthttp.Client
-		JWTUserClaimPath    string
-		JWTRoleClaimPath    string
-		RoleFromHeader      string
-		proxy               string
-		ClientTimeout       int
-		MaxConnsPerHost     int
-		ReadTimeout         int
-		WriteTimeout        int
-		MaxIdleConnDuration int
-		RoleRateLimit       bool
-		DisableTLSVerify    bool
+		GQLClient            *graphql.BaseClient
+		FastProxyClient      *fasthttp.Client
+		JWTUserClaimPath     string
+		JWTRoleClaimPath     string
+		RoleFromHeader       string
+		proxy                string
+		ClientTimeout        int
+		MaxConnsPerHost      int
+		ReadTimeout          int
+		WriteTimeout         int
+		MaxIdleConnDuration  int
+		RetryBaseDelayMs     int // initial backoff delay in milliseconds (default 500)
+		RetryMaxDelayMs      int // maximum backoff delay in milliseconds (default 10000)
+		RoleRateLimit        bool
+		DisableTLSVerify     bool
 	}
 	Server struct {
 		HostGraphQL         string