go/worker/compute: Simplify I/O root commit

[kostko]

This also avoids an intermediate committed IO root which complicates the required database layout.

[codecov]

Codecov Report

Attention: 222 lines in your changes are missing coverage. Please review.

Comparison is base (191d346) 66.91% compared to head (cb75520) 66.85%.
Report is 6 commits behind head on master.

Files	Patch %	Lines
go/keymanager/secrets/grpc.go	53.33%	62 Missing and 22 partials ⚠️
...nsensus/cometbft/apps/keymanager/secrets/status.go	80.10%	26 Missing and 11 partials ⚠️
...sensus/cometbft/apps/keymanager/secrets/genesis.go	48.88%	16 Missing and 7 partials ⚠️
go/consensus/cometbft/keymanager/secrets/client.go	72.94%	16 Missing and 7 partials ⚠️
...o/consensus/cometbft/apps/keymanager/keymanager.go	65.38%	10 Missing and 8 partials ⚠️
.../consensus/cometbft/apps/keymanager/secrets/ext.go	70.58%	7 Missing and 3 partials ⚠️
go/keymanager/secrets/api.go	82.22%	6 Missing and 2 partials ⚠️
.../consensus/cometbft/apps/keymanager/secrets/txs.go	64.70%	0 Missing and 6 partials ⚠️
go/oasis-node/cmd/keymanager/keymanager.go	76.47%	3 Missing and 1 partial ⚠️
go/consensus/cometbft/apps/keymanager/genesis.go	60.00%	1 Missing and 1 partial ⚠️
... and 4 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5553      +/-   ##
==========================================
- Coverage   66.91%   66.85%   -0.07%     
==========================================
  Files         539      546       +7     
  Lines       56883    56861      -22     
==========================================
- Hits        38064    38015      -49     
- Misses      14379    14410      +31     
+ Partials     4440     4436       -4     

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