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/bitcoin-chainstate.cpp

@@ -68,7 +68,6 @@ int main(int argc, char* argv[])
     // performing the check with the signature cache.
     kernel::ValidationCacheSizes validation_cache_sizes{};
     Assert(InitSignatureCache(validation_cache_sizes.signature_cache_bytes));
-    Assert(InitScriptExecutionCache(validation_cache_sizes.script_execution_cache_bytes));
 
     ValidationSignals validation_signals{std::make_unique<util::ImmediateTaskRunner>()};