runtime: Reduce maximum RHP message size

[kostko]

Fixes #2213

Message size is reduced based on benchmark metrics where messages never exceeded 3 MiB even with large batches.

Also enforces maximum batch sizes at compute nodes.

[codecov]

Codecov Report

Merging #3139 into master will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3139      +/-   ##
==========================================
+ Coverage   68.91%   68.98%   +0.06%     
==========================================
  Files         375      375              
  Lines       37050    37060      +10     
==========================================
+ Hits        25533    25565      +32     
+ Misses       8268     8251      -17     
+ Partials     3249     3244       -5     

Impacted Files	Coverage Δ
go/common/cbor/codec.go	78.37% <ø> (ø)
go/runtime/transaction/transaction.go	78.03% <100.00%> (+3.48%)	⬆️
go/worker/compute/executor/committee/batch.go	69.23% <100.00%> (ø)
go/worker/compute/executor/committee/node.go	65.10% <100.00%> (+1.07%)	⬆️
go/storage/mkvs/tree.go	89.28% <0.00%> (-3.58%)	⬇️
go/worker/common/committee/node.go	75.70% <0.00%> (-2.83%)	⬇️
go/runtime/client/watcher.go	73.84% <0.00%> (-1.54%)	⬇️
go/consensus/tendermint/roothash/roothash.go	72.72% <0.00%> (-1.38%)	⬇️
go/storage/client/client.go	74.16% <0.00%> (-1.25%)	⬇️
go/worker/compute/txnscheduler/committee/node.go	64.86% <0.00%> (-1.21%)	⬇️
... and 19 more

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