triedb/pathdb: improve perf by separating nodes map

[weiihann]

Description

This PR refactors the nodeSet structure in the path database to use separate maps for account and storage trie nodes, resulting in performance improvements. The change maintains the same API while optimizing the internal data structure.

Motivation

The original implementation used a single nested map structure for both account and storage nodes:

nodes map[common.Hash]map[string]*trienode.Node // node set, mapped by owner and path

This required two map lookups for account nodes (first by owner hash, then by path). By separating account nodes into their own dedicated map, we can eliminate one level of indirection for account operations.

Changes

Refactored nodeSet to use two separate maps:

accountNodes map[string]*trienode.Node // for account trie nodes
storageNodes map[common.Hash]map[string]*trienode.Node // for storage trie nodes

This change maintains full backward compatibility as all method signatures remain unchanged. The refactoring is purely internal to the nodeSet structure.

Benchmark Results

goos: darwin
goarch: arm64
pkg: github.com/ethereum/go-ethereum/triedb/pathdb
cpu: Apple M3 Pro
                                                          │   old.txt    │               new.txt                │
                                                          │    sec/op    │    sec/op     vs base                │
Search128Layers-11                                          9.890µ ± 12%   6.651µ ± 16%  -32.75% (p=0.000 n=10)
Search512Layers-11                                          46.13µ ±  5%   32.45µ ±  2%  -29.66% (p=0.000 n=10)
Search1Layer-11                                             51.03n ±  1%   43.95n ±  5%  -13.86% (p=0.000 n=10)
Persist-11                                                  97.51m ±  9%   84.45m ± 11%  -13.39% (p=0.000 n=10)
AccountIteratorTraversal/binary_iterator_keys-11            9.184µ ±  1%   9.336µ ± 25%   +1.66% (p=0.005 n=10)
AccountIteratorTraversal/binary_iterator_values-11          14.05µ ± 12%   13.88µ ±  0%   -1.19% (p=0.000 n=10)
AccountIteratorTraversal/fast_iterator_keys-11              8.479µ ± 10%   7.881µ ±  1%   -7.05% (p=0.000 n=10)
AccountIteratorTraversal/fast_iterator_values-11            8.326µ ±  4%   8.066µ ±  2%   -3.13% (p=0.001 n=10)
AccountIteratorLargeBaselayer/binary_iterator_(keys)-11     11.05m ±  3%   10.59m ±  0%   -4.17% (p=0.000 n=10)
AccountIteratorLargeBaselayer/binary_iterator_(values)-11   17.45m ±  0%   16.83m ±  1%   -3.53% (p=0.000 n=10)
AccountIteratorLargeBaselayer/fast_iterator_(keys)-11       133.8µ ±  0%   131.2µ ±  0%   -1.96% (p=0.000 n=10)
AccountIteratorLargeBaselayer/fast_iterator_(values)-11     135.8µ ±  2%   133.2µ ±  3%   -1.89% (p=0.015 n=10)
geomean                                                     80.35µ         72.35µ         -9.96%

[rjl493456442]

Let's merge the overall performance first before merging it.