Update SA tool and soothe them

The commit introduces `is_string` function in a condition in `MethodSignatureString.php`. Several tools in `composer.lock` have been updated to newer versions, including packages like `amphp/amp`, `amphp/byte-stream`, and others. This commit thus refactors the code for improved validation and updates dependencies for enhanced project features.

sl-src/CacheReader.php

@@ -15,6 +15,7 @@
 use function array_merge;
 use function assert;
 use function filemtime;
+use function is_string;
 use function max;
 use function rawurlencode;
 
@@ -161,7 +162,7 @@ private function getLastModification(ReflectionClass $class): int  // @phpstan-i
         $parent = $class->getParentClass();
 
         $lastModification =  max(array_merge(
-            [$filename ? filemtime($filename) : 0],
+            [is_string($filename) ? filemtime($filename) : 0],
             array_map(function (ReflectionClass $reflectionTrait): int {
                 return $this->getTraitLastModificationTime($reflectionTrait);
             }, $class->getTraits()),
@@ -185,7 +186,7 @@ private function getTraitLastModificationTime(ReflectionClass $reflectionTrait):
         }
 
         $lastModificationTime = max(array_merge(
-            [$fileName ? filemtime($fileName) : 0],
+            [is_string($fileName) ? filemtime($fileName) : 0],
             array_map(function (ReflectionClass $reflectionTrait): int {
                 return $this->getTraitLastModificationTime($reflectionTrait);
             }, $reflectionTrait->getTraits())

src/MethodSignatureString.php

@@ -10,6 +10,7 @@
 
 use function implode;
 use function is_numeric;
+use function is_string;
 use function preg_replace;
 use function sprintf;
 use function str_replace;
@@ -40,7 +41,7 @@ public function get(ReflectionMethod $method): string
 
         // PHPDocを取得
         $docComment = $method->getDocComment();
-        if ($docComment) {
+        if (is_string($docComment)) {
             $signatureParts[] = $docComment . PHP_EOL;
         }