docs: Message pack information.

[winder]

Summary

Was having a discussion about message pack and learned a couple things. Writing them down for posterity.

Test Plan

N/A

[codecov]

Codecov Report

Merging #5160 (41e0de1) into master (a688c23) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5160      +/-   ##
==========================================
+ Coverage   53.44%   53.48%   +0.03%     
==========================================
  Files         431      431              
  Lines       54364    54364              
==========================================
+ Hits        29056    29074      +18     
+ Misses      23053    23040      -13     
+ Partials     2255     2250       -5     

Impacted Files	Coverage Δ
ledger/testing/randomAccounts.go	55.65% <0.00%> (-1.23%)	⬇️
cmd/tealdbg/debugger.go	71.65% <0.00%> (-0.79%)	⬇️
data/transactions/logic/assembler.go	87.89% <0.00%> (-0.13%)	⬇️
ledger/tracker.go	75.10% <0.00%> (ø)
network/wsNetwork.go	65.34% <0.00%> (+0.18%)	⬆️
ledger/acctonline.go	79.16% <0.00%> (+0.52%)	⬆️
ledger/catchpointtracker.go	58.69% <0.00%> (+0.78%)	⬆️
catchup/service.go	70.35% <0.00%> (+1.41%)	⬆️
network/wsPeer.go	68.27% <0.00%> (+2.29%)	⬆️

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[onetechnical]

Thanks for this!