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/app/AMMCalc_test.cpp

@@ -43,10 +43,14 @@ class AMMCalc_test : public beast::unit_test::suite
             if (delimited)
                 *delimited = (match[3] != "");
             if (match[1] == "XRP")
+            {
                 return XRP(std::stoll(match[2]));
-            // drops
-            else if (match[1] == "XRPA")
+                // drops
+            }
+            if (match[1] == "XRPA")
+            {
                 return XRPAmount{std::stoll(match[2])};
+            }
             return amountFromString(gw[match[1]].asset(), match[2]);
         }
         return std::nullopt;
@@ -120,7 +124,9 @@ class AMMCalc_test : public beast::unit_test::suite
                     break;
             }
             else
+            {
                 return std::nullopt;
+            }
         }
         return rates;
     }
@@ -398,13 +404,17 @@ class AMMCalc_test : public beast::unit_test::suite
                                 env.current()->rules(),
                                 beast::Journal(beast::Journal::getNullSink()));
                             ammOffer)
+                        {
                             std::cout << "amm offer: " << toString(ammOffer->in) << " "
                                       << toString(ammOffer->out)
                                       << "\nnew pool: " << toString(pool->first.in + ammOffer->in)
                                       << " " << toString(pool->first.out - ammOffer->out)
                                       << std::endl;
+                        }
                         else
+                        {
                             std::cout << "can't change the pool's SP quality" << std::endl;
+                        }
                         return true;
                     }
                 }