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/jtx/impl/fee.cpp

@@ -14,9 +14,13 @@ fee::operator()(Env& env, JTx& jt) const
     jt.fill_fee = false;
     assert(!increment_ || !amount_);
     if (increment_)
+    {
         jt[sfFee] = STAmount(env.current()->fees().increment).getJson();
+    }
     else if (amount_)
+    {
         jt[sfFee] = amount_->getJson(JsonOptions::none);
+    }
 }
 
 }  // namespace jtx