refactor: Add simple clang-tidy readability checks (#6556)

This change enables the following clang-tidy checks:
-  readability-avoid-nested-conditional-operator,
-  readability-avoid-return-with-void-value,
-  readability-braces-around-statements,
-  readability-const-return-type,
-  readability-container-contains,
-  readability-container-size-empty,
-  readability-else-after-return,
-  readability-make-member-function-const,
-  readability-redundant-casting,
-  readability-redundant-inline-specifier,
-  readability-redundant-member-init,
-  readability-redundant-string-init,
-  readability-reference-to-constructed-temporary,
-  readability-static-definition

src/test/protocol/STParsedJSON_test.cpp

@@ -894,7 +894,7 @@ class STParsedJSON_test : public beast::unit_test::suite
             BEAST_EXPECT(obj.object->isFieldPresent(sfPublicKey));
             auto const& blob =
                 obj.object->getFieldVL(sfPublicKey);  // NOLINT(bugprone-unchecked-optional-access)
-            BEAST_EXPECT(blob.size() == 0);
+            BEAST_EXPECT(blob.empty());
         }
 
         // Test lowercase hex string for blob
@@ -975,7 +975,7 @@ class STParsedJSON_test : public beast::unit_test::suite
             BEAST_EXPECT(obj.object->isFieldPresent(sfHashes));
             auto const& vec =
                 obj.object->getFieldV256(sfHashes);  // NOLINT(bugprone-unchecked-optional-access)
-            BEAST_EXPECT(vec.size() == 0);
+            BEAST_EXPECT(vec.empty());
         }
 
         // Test array with invalid hex string (should fail)