fix(config): support float64 env values in getDetailsFromEnv

The generic typed env reader only handled string/int/bool; any float64 key
fell through to default, so CIRCUIT_FAILURE_RATIO, CIRCUIT_BACKOFF_
MULTIPLIER and RETRY_BUDGET_TOKENS_PER_SEC were silently impossible to
override via environment (always the compile-time default).

Add a float64 case mirroring the int one: parse the GMP_ prefixed key,
then the plain key, else the default (envutil has no GetFloat).

Test: extended Test_getDetailsFromEnv with float-valid and float-malformed
cases.

main.go

@@ -71,6 +71,22 @@ func getDetailsFromEnv[T any](key string, defaultValue T) T {
 			return any(boolVal).(T)
 		}
 		return any(envutil.GetBool(key, v)).(T)
+	case float64:
+		// envutil has no GetFloat; handle the GMP_ prefixed and plain keys
+		// directly. Previously float64 env values (CIRCUIT_FAILURE_RATIO,
+		// CIRCUIT_BACKOFF_MULTIPLIER, RETRY_BUDGET_TOKENS_PER_SEC) fell into
+		// default and were silently impossible to configure.
+		if val, ok := os.LookupEnv(prefixedKey); ok {
+			if f, err := strconv.ParseFloat(val, 64); err == nil {
+				return any(f).(T)
+			}
+		}
+		if val, ok := os.LookupEnv(key); ok {
+			if f, err := strconv.ParseFloat(val, 64); err == nil {
+				return any(f).(T)
+			}
+		}
+		return defaultValue
 	default:
 		return defaultValue
 	}

main_test.go

@@ -154,6 +154,8 @@ func (suite *Tests) Test_getDetailsFromEnv() {
 		{"default", "envValue", "string value", "TEST_STRING", "envValue"},
 		{0, 123, "int value", "TEST_INT", "123"},
 		{false, true, "bool value", "TEST_BOOL", "true"},
+		{0.5, 0.25, "float value", "TEST_FLOAT", "0.25"},
+		{0.5, 0.5, "float default on malformed value", "TEST_FLOAT_BAD", "not-a-number"},
 		{"default", "default", "default value", "NON_EXISTENT", ""},
 	}