core/state/snapshot: check difflayer staleness early

[ucwong]

This PR adds a staleness-check to AccountRLP, before checking the bloom-filter and potentially going directly into the disklayer.

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[codecov]

Codecov Report

Merging #1548 (0344833) into master (c36f17b) will decrease coverage by 0.03%.
The diff coverage is 47.01%.

❗ Current head 0344833 differs from pull request most recent head bd70bd2. Consider uploading reports for the commit bd70bd2 to get more accurate results

@@            Coverage Diff             @@
##           master    #1548      +/-   ##
==========================================
- Coverage   52.68%   52.65%   -0.03%     
==========================================
  Files         476      479       +3     
  Lines       59723    59806      +83     
==========================================
+ Hits        31463    31489      +26     
- Misses      25896    25937      +41     
- Partials     2364     2380      +16     

Impacted Files	Coverage Δ
client/ctxc_client.go	8.13% <0.00%> (-0.06%)	⬇️
cmd/cortex/main.go	21.73% <ø> (ø)
cmd/utils/flags.go	1.85% <0.00%> (-0.02%)	⬇️
core/asm/compiler.go	62.30% <0.00%> (+0.47%)	⬆️
crypto/kzg4844/kzg4844_ckzg_nocgo.go	0.00% <0.00%> (ø)
ctxc/api_backend.go	0.00% <0.00%> (ø)
p2p/msgrate/msgrate.go	14.28% <0.00%> (ø)
core/state/snapshot/difflayer.go	72.06% <14.28%> (-1.80%)	⬇️
crypto/kzg4844/kzg4844.go	34.48% <34.48%> (ø)
crypto/kzg4844/kzg4844_gokzg.go	64.70% <64.70%> (ø)
... and 7 more

... and 16 files with indirect coverage changes