[TASK] Add native type declarations for anonymous functions

Also make then static if possible.

CHANGELOG.md

@@ -19,7 +19,7 @@ Please also have a look at our
 ### Changed
 
 - Use more native type declarations and strict mode
-  (#641, #772, #774, #778, #804)
+  (#641, #772, #774, #778, #804, #841)
 - Add visibility to all class/interface constants (#469)
 
 ### Deprecated

src/CSSList/CSSList.php

@@ -413,7 +413,7 @@ protected function renderListContents(OutputFormat $oOutputFormat)
             $oNextLevel = $oOutputFormat->nextLevel();
         }
         foreach ($this->aContents as $oContent) {
-            $sRendered = $oOutputFormat->safely(function () use ($oNextLevel, $oContent) {
+            $sRendered = $oOutputFormat->safely(function () use ($oNextLevel, $oContent): string {
                 return $oContent->render($oNextLevel);
             });
             if ($sRendered === null) {

src/RuleSet/RuleSet.php

@@ -162,7 +162,7 @@ public function getRules($mRule = null)
                 $aResult = \array_merge($aResult, $aRules);
             }
         }
-        \usort($aResult, function (Rule $first, Rule $second) {
+        \usort($aResult, static function (Rule $first, Rule $second): int {
             if ($first->getLineNo() === $second->getLineNo()) {
                 return $first->getColNo() - $second->getColNo();
             }
@@ -266,7 +266,7 @@ protected function renderRules(OutputFormat $oOutputFormat)
         $oNextLevel = $oOutputFormat->nextLevel();
         foreach ($this->aRules as $aRules) {
             foreach ($aRules as $rule) {
-                $sRendered = $oNextLevel->safely(function () use ($rule, $oNextLevel) {
+                $sRendered = $oNextLevel->safely(function () use ($rule, $oNextLevel): string {
                     return $rule->render($oNextLevel);
                 });
                 if ($sRendered === null) {