perf: cache repeated storage trie lookups

[Qumeric]

Stacked on #664.

Add one-entry caches for address hashes and storage-trie references in WitnessDb. REVM storage accesses commonly arrive in runs for the same account, so this avoids repeated address Keccak operations and storage-trie hash-table lookups without adding a general-purpose cache.

WitnessDb borrows the backing Ethereum state immutably, so cached trie references cannot become stale during execution.

Benchmark results

Block 24001988, RVR execution. The attribution points 29811230163 and 29750974205 differ only by this cache change:

metric	before cache	with cache	delta
execute_metered_insns	644,105,893	640,063,687	−4,042,206 (−0.63%)
metered_rows_unpadded	927,502,024	923,404,883	−4,097,141 (−0.44%)
metered_main_cells_unpadded	47,413,076,953	46,872,486,323	−540,590,630 (−1.14%)
metered_interaction_cells_unpadded	14,470,853,876	14,381,062,111	−89,791,765 (−0.62%)

Block 24003902

RVR execution: #664, this PR.

metric	#664	this PR	delta
execute_metered_insns	512,092,682	511,200,060	−892,622 (−0.17%)
metered_rows_unpadded	692,838,316	691,954,121	−884,195 (−0.13%)
metered_main_cells_unpadded	30,149,424,975	30,054,639,856	−94,785,119 (−0.31%)
metered_interaction_cells_unpadded	11,994,791,134	11,974,365,720	−20,425,414 (−0.17%)
metered_memory_unpadded_bytes	575,266,433,578	574,055,559,407	−1,210,874,171 (−0.21%)
memory-triggered segment cuts	51	51	0

[Qumeric]

Superseded by #683 — same change, reparented onto develop-v2.1.0. It touches only crates/stateless-executor/src/io.rs, so being stacked mid-series was incidental; it applies to develop with no conflicts and an identical diff.