core/vm/program: evm bytecode-building utility ethereum#30725

In many cases, there is a need to create somewhat nontrivial bytecode. A
recent example is the verkle statetests, where we want a `CREATE2`- op
to create a contract, which can then be invoked, and when invoked does a
selfdestruct-to-self.

It is overkill to go full solidity, but it is also a bit tricky do
assemble this by concatenating bytes. This PR takes an approach that
has been used in in goevmlab for several years.

Using this utility, the case can be expressed as:
```golang
	// Some runtime code
	runtime := program.New().Ops(vm.ADDRESS, vm.SELFDESTRUCT).Bytecode()
	// A constructor returning the runtime code
	initcode := program.New().ReturnData(runtime).Bytecode()
	// A factory invoking the constructor
	outer := program.New().Create2AndCall(initcode, nil).Bytecode()
```

We have a lot of places in the codebase where we concatenate bytes, cast
from `vm.OpCode` . By taking tihs approach instead, thos places can be made a
bit more maintainable/robust.

Author: holiman

core/state/database.go

@@ -132,6 +132,12 @@ func NewDatabase(db ethdb.Database) Database {
 	return NewDatabaseWithConfig(db, nil)
 }
 
+// NewDatabaseForTesting is similar to NewDatabase, but it initializes the caching
+// db by using an ephemeral memory db with default config for testing.
+func NewDatabaseForTesting() Database {
+	return NewDatabase(rawdb.NewMemoryDatabase())
+}
+
 // NewDatabaseWithConfig creates a backing store for state. The returned database
 // is safe for concurrent use and retains a lot of collapsed RLP trie nodes in a
 // large memory cache.