kernel: De-globalize script execution cache

Move its ownership to the ChainstateManager class.

Next to simplifying usage of the kernel library by no longer requiring
manual setup of the cache prior to using validation code, it also slims
down the amount of memory allocated by BasicTestingSetup.

src/node/chainstatemanager_args.cpp

@@ -56,6 +56,15 @@ util::Result<void> ApplyArgsManOptions(const ArgsManager& args, ChainstateManage
     opts.worker_threads_num = std::clamp(script_threads - 1, 0, MAX_SCRIPTCHECK_THREADS);
     LogPrintf("Script verification uses %d additional threads\n", opts.worker_threads_num);
 
+    if (auto max_size = args.GetIntArg("-maxsigcachesize")) {
+        // 1. When supplied with a max_size of 0, both the signature cache and
+        //    script execution cache create the minimum possible cache (2
+        //    elements). Therefore, we can use 0 as a floor here.
+        // 2. Multiply first, divide after to avoid integer truncation.
+        size_t clamped_size_each = std::max<int64_t>(*max_size, 0) * (1 << 20) / 2;
+        opts.script_execution_cache_bytes = clamped_size_each;
+    }
+
     return {};
 }
 } // namespace node