trie: reduce the memory allocation in trie hashing

[rjl493456442]

This pull request optimizes trie hashing by reducing memory allocation overhead. Specifically:

• define a fullNodeEncoder pool to reuse encoders and avoid memory allocations.
• simplify the encoding logic for shortNode and fullNode by getting rid of the Go interfaces.

---

Benchmark results

• The memory allocation has been reduced significantly
• The CPU IOWait is constantly higher with unknown reason
• The overall performance is slightly slower

Memory profile

[[ PR ]]
(pprof) top10
Showing nodes accounting for 8512.51GB, 46.05% of 18486.12GB total
Dropped 2316 nodes (cum <= 92.43GB)
Showing top 10 nodes out of 246
      flat  flat%   sum%        cum   cum%
 2131.23GB 11.53% 11.53%  4212.13GB 22.79%  github.com/ethereum/go-ethereum/trie.decodeFull
 2081.41GB 11.26% 22.79%  2081.43GB 11.26%  github.com/ethereum/go-ethereum/trie.decodeRef
 1227.24GB  6.64% 29.43%  1227.24GB  6.64%  github.com/ethereum/go-ethereum/rlp.(*encBuffer).makeBytes
 1016.72GB  5.50% 34.93%  1016.72GB  5.50%  github.com/ethereum/go-ethereum/trie.(*tracer).onRead (inline)
     385GB  2.08% 37.01%   418.67GB  2.26%  github.com/ethereum/go-ethereum/core/state.newObject
  366.55GB  1.98% 38.99%   676.40GB  3.66%  github.com/ethereum/go-ethereum/core/state.(*stateObject).GetCommittedState
  342.26GB  1.85% 40.84%   425.03GB  2.30%  github.com/ethereum/go-ethereum/core/state.(*stateObject).finalise
  340.53GB  1.84% 42.69%  3821.35GB 20.67%  github.com/ethereum/go-ethereum/trie.(*Trie).insert
  340.36GB  1.84% 44.53%   340.36GB  1.84%  github.com/ethereum/go-ethereum/core/vm.codeBitmap
  281.20GB  1.52% 46.05%   281.20GB  1.52%  github.com/ethereum/go-ethereum/trie.keybytesToHex (inline)

[[ Master ]]

(pprof) alloc_space
(pprof) top10
Showing nodes accounting for 13090.96GB, 54.01% of 24239.01GB total
Dropped 2401 nodes (cum <= 121.20GB)
Showing top 10 nodes out of 221
      flat  flat%   sum%        cum   cum%
 4398.55GB 18.15% 18.15%  5110.55GB 21.08%  github.com/ethereum/go-ethereum/trie.(*hasher).hashFullNodeChildren
 2248.19GB  9.28% 27.42%  4442.15GB 18.33%  github.com/ethereum/go-ethereum/trie.decodeFull
 2194.50GB  9.05% 36.48%  2194.51GB  9.05%  github.com/ethereum/go-ethereum/trie.decodeRef
 1301.95GB  5.37% 41.85%  1301.95GB  5.37%  github.com/ethereum/go-ethereum/rlp.(*encBuffer).makeBytes
 1073.52GB  4.43% 46.28%  1073.52GB  4.43%  github.com/ethereum/go-ethereum/trie.(*tracer).onRead (inline)
  405.73GB  1.67% 47.95%   441.01GB  1.82%  github.com/ethereum/go-ethereum/core/state.newObject
  384.59GB  1.59% 49.54%   709.87GB  2.93%  github.com/ethereum/go-ethereum/core/state.(*stateObject).GetCommittedState
  365.17GB  1.51% 51.04%   365.17GB  1.51%  github.com/ethereum/go-ethereum/core/vm.codeBitmap
  364.32GB  1.50% 52.55%   452.82GB  1.87%  github.com/ethereum/go-ethereum/core/state.(*stateObject).finalise
  354.43GB  1.46% 54.01%  4021.69GB 16.59%  github.com/ethereum/go-ethereum/trie.(*Trie).insert
(pprof)

[rjl493456442]

After running a bit more, it turns out the IOwait is not relevant with the change.

The PR is slightly slower though.

[omerfirmak]

Could we have made the return type here and hashNode a [32]byte? It probably wouldn't save much on the total size of allocations, but it will reduce the number of individual allocations.