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/rpc/Simulate_test.cpp

@@ -59,7 +59,7 @@ class Simulate_test : public beast::unit_test::suite
         int const expectedSequence,
         XRPAmount const& expectedFee)
     {
-        return checkBasicReturnValidity(
+        checkBasicReturnValidity(
             result, tx, expectedSequence, expectedFee.jsonClipped().asString());
     }