cuckoocache: Return approximate memory size

Returning the approximate total size eliminates the need for
InitS*Cache() to do nElems*sizeof(uint256). The cuckoocache has a better
idea of this information.

src/validation.cpp

@@ -1656,7 +1656,7 @@ bool CScriptCheck::operator()() {
 static CuckooCache::cache<uint256, SignatureCacheHasher> g_scriptExecutionCache;
 static CSHA256 g_scriptExecutionCacheHasher;
 
-void InitScriptExecutionCache() {
+bool InitScriptExecutionCache() {
     // Setup the salted hasher
     uint256 nonce = GetRandHash();
     // We want the nonce to be 64 bytes long to force the hasher to process
@@ -1667,9 +1667,13 @@ void InitScriptExecutionCache() {
     // nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
     // setup_bytes creates the minimum possible cache (2 elements).
     size_t nMaxCacheSize = std::min(std::max((int64_t)0, gArgs.GetIntArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
-    size_t nElems = g_scriptExecutionCache.setup_bytes(nMaxCacheSize);
+
+    auto setup_results = g_scriptExecutionCache.setup_bytes(nMaxCacheSize);
+
+    const auto [num_elems, approx_size_bytes] = setup_results;
     LogPrintf("Using %zu MiB out of %zu/2 requested for script execution cache, able to store %zu elements\n",
-            (nElems*sizeof(uint256)) >>20, (nMaxCacheSize*2)>>20, nElems);
+              approx_size_bytes >> 20, (nMaxCacheSize * 2) >> 20, num_elems);
+    return true;
 }
 
 /**