go/consensus/tendermint: Make sure DBs are only closed during cleanup

[kostko]

Tendermint Core will close the block/state store DBs during Stop which
can make certain in-flight queries trigger a panic due to the database
being already closed.

This commit introduces a DB wrapper that enables us to defer closing
the DB until Cleanup is called (as at that point all of the services
have already been stopped).

[codecov]

Codecov Report

Merging #4823 (27f763c) into master (5fd5b80) will increase coverage by 0.03%.
The diff coverage is 76.47%.

❗ Current head 27f763c differs from pull request most recent head c5375f6. Consider uploading reports for the commit c5375f6 to get more accurate results

@@            Coverage Diff             @@
##           master    #4823      +/-   ##
==========================================
+ Coverage   66.64%   66.68%   +0.03%     
==========================================
  Files         451      452       +1     
  Lines       50310    50320      +10     
==========================================
+ Hits        33529    33554      +25     
- Misses      12620    12623       +3     
+ Partials     4161     4143      -18     

Impacted Files	Coverage Δ
go/consensus/tendermint/full/light.go	59.25% <0.00%> (-6.13%)	⬇️
go/consensus/tendermint/full/common.go	66.42% <57.14%> (-0.73%)	⬇️
go/consensus/tendermint/db/closer.go	100.00% <100.00%> (ø)
go/consensus/tendermint/full/archive.go	77.39% <100.00%> (+2.60%)	⬆️
go/consensus/tendermint/full/full.go	65.04% <100.00%> (+0.07%)	⬆️
go/runtime/host/sandbox/sandbox.go	60.82% <0.00%> (-6.53%)	⬇️
go/common/grpc/auth/auth.go	94.73% <0.00%> (-5.27%)	⬇️
.../worker/compute/executor/committee/transactions.go	86.36% <0.00%> (-4.55%)	⬇️
go/runtime/host/multi/multi.go	70.58% <0.00%> (-4.42%)	⬇️
go/common/sgx/common.go	66.01% <0.00%> (-3.89%)	⬇️
... and 29 more

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