runtime: Use separate cache for checking transactions

[kostko]

This allows calling both check and execute methods against the same runtime
instance.

[codecov]

Codecov Report

Merging #3191 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3191      +/-   ##
==========================================
- Coverage   68.06%   68.05%   -0.02%     
==========================================
  Files         380      380              
  Lines       36620    36620              
==========================================
- Hits        24925    24920       -5     
  Misses       8480     8480              
- Partials     3215     3220       +5     

Impacted Files	Coverage Δ
go/worker/common/p2p/dispatch.go	67.28% <0.00%> (-7.48%)	⬇️
go/common/grpc/policy/policy.go	64.38% <0.00%> (-6.85%)	⬇️
go/consensus/tendermint/full/services.go	82.81% <0.00%> (-5.47%)	⬇️
go/storage/metrics.go	81.08% <0.00%> (-4.06%)	⬇️
go/common/sgx/common.go	68.68% <0.00%> (-4.05%)	⬇️
.../consensus/tendermint/apps/roothash/state/state.go	68.62% <0.00%> (-3.93%)	⬇️
go/worker/keymanager/handler.go	60.37% <0.00%> (-3.78%)	⬇️
go/storage/api/root_cache.go	77.77% <0.00%> (-3.18%)	⬇️
go/worker/storage/service_external.go	57.35% <0.00%> (-2.95%)	⬇️
...consensus/tendermint/apps/roothash/transactions.go	59.45% <0.00%> (-2.71%)	⬇️
... and 23 more

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[ptrus]

Seems to work, thanks!