Fix the following linter warning:
```
pkg/rpc/client/wsclient.go:99:18 govet copylocks: literal copies lock value from *cl: github.com/nspcc-dev/neo-go/pkg/rpc/client.Client contains sync.RWMutex
```
1. Keep initDone check only for the places where cache is directly accessed.
We don't need to check it in other places, otherwise we have a mess of
duplicating checks.
2. Fix bug in code related to block deserialisation. There's no magic, so
checking that initialisation is done is not enough for proper block
deserialisation. We need to manually fill StateRootEnabled field.
3. Since transaction doesn't need network magic to compute its hash, we don't
need to perform Client initialisation before transaction-related requests.
4. Check that cache is initialised before accessing network magic.
5. Refactor the way Policy contract hash is fetched for Client requests.
We don't really need Client initialisation for that, it's OK to fetch Policy
hash on-the-fly.
When execution fails it's the only way to change the prompt showing the
last executed instruction. Example:
```
NEO-GO-VM > loadgo examples/engine/engine.go
READY: loaded 117 instructions
NEO-GO-VM 0 > run
Error: at instruction 3 (SYSCALL): failed to invoke syscall 805851437: syscall not found
NEO-GO-VM 8 > parse
Error: missing argument
NEO-GO-VM 8 > parse 123
Integer to Hex 7b
Integer to Base64 ew==
String to Hex 313233
String to Base64 MTIz
NEO-GO-VM 8 > unload
NEO-GO-VM > exit
```
We don't have a need to iterate over them at the moment, but since we're
changing the DB format in the next release anyway let's add this ability also,
just in case.
It couldn't be done previously with two maps and mixed storage, but now all of
the storage changes are located in a single map, so it's trivial to do exact
slice allocations and avoid string->[]byte conversions.
Private DAO is only used in a single thread which means we can safely reuse
key/data buffers most of the time and handle it all in DAO.
Doesn't affect any benchmarks.
Most of the time we don't need locking on the higher-level stores and we drop
them after Persist, so that's what private MemCachedStore is for.
It doesn't improve things in any noticeable way, some ~1% can be observed in
neo-bench under various loads and even less than that in chain processing. But
it seems to be a bit better anyway (less allocations, less locks).
They never return errors, so their interface should reflect that. This allows
to remove quite a lot of useless and never tested code.
Notice that Get still does return an error. It can be made not to do that, but
usually we need to differentiate between successful/unsuccessful accesses
anyway, so this doesn't help much.
Simple and dumb as it is, this allows to separate contract storage from other
things and dramatically improve Seek() time over storage (even though it's
still unordered!) which in turn improves block processing speed.
LevelDB LevelDB (KeepOnlyLatest) BoltDB BoltDB (KeepOnlyLatest)
Master real 16m27,936s real 10m9,440s real 16m39,369s real 8m1,227s
user 20m12,619s user 26m13,925s user 18m9,162s user 18m5,846s
sys 2m56,377s sys 1m32,051s sys 9m52,576s sys 2m9,455s
2 maps real 10m49,495s real 8m53,342s real 11m46,204s real 5m56,043s
user 14m19,922s user 24m6,225s user 13m25,691s user 15m4,694s
sys 1m53,021s sys 1m23,006s sys 4m31,735s sys 2m8,714s
neo-bench performance is mostly unaffected, ~0.5% for 1-1 test and 4% for
10K-10K test both fall within regular test error range.
