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/server/ServerStatus_test.cpp

@@ -616,9 +616,8 @@ class ServerStatus_test : public beast::unit_test::suite, public beast::test::en
         boost::system::error_code ec;
         doRequest(yield, makeWSUpgrade(ip, port), ip, port, true, resp, ec);
         BEAST_EXPECT(resp.result() == boost::beast::http::status::switching_protocols);
-        BEAST_EXPECT(resp.find("Upgrade") != resp.end() && resp["Upgrade"] == "websocket");
-        BEAST_EXPECT(
-            resp.find("Connection") != resp.end() && boost::iequals(resp["Connection"], "upgrade"));
+        BEAST_EXPECT(resp.contains("Upgrade") && resp["Upgrade"] == "websocket");
+        BEAST_EXPECT(resp.contains("Connection") && boost::iequals(resp["Connection"], "upgrade"));
     }
 
     void