Integrate end to end hashed chain exchange with F3

[masih]

Integrate the chain exchange mechanism with F3 host and runner. But without touching the core GPBFT.

The implementation here leaves two major TODOs: 1) chain broadcasting mechanism (currently coupled to GPBFT message broadcast), and 2) partial message validation prior to buffering (currently skipped entirely but with capped buffer sizes and re-validation by core GPBFT once the messages are complete).

The integration introduces the concept of Partial GMessage: a GMessage with chains replaced with the key to the chain. The work introduces a buffer and refill mechanism that listens to the chains discovered, un-buffers the messages having re-constructed their original GMessage and feeds them to the participation using the existing event loop.

Part of #792

[Kubuxu]

Conceptually SGTM, will do another dive latter after I think it over.

[codecov]

Codecov Report

Attention: Patch coverage is 68.35443% with 125 lines in your changes missing coverage. Please review.

Project coverage is 69.34%. Comparing base (c4b5f6a) to head (09d3cb7).

Files with missing lines	Patch %	Lines
cbor_gen.go	28.76%	35 Missing and 17 partials ⚠️
partial_msg.go	81.81%	32 Missing and 6 partials ⚠️
host.go	54.54%	27 Missing and 8 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #816      +/-   ##
==========================================
+ Coverage   68.82%   69.34%   +0.52%     
==========================================
  Files          81       83       +2     
  Lines        8307     8662     +355     
==========================================
+ Hits         5717     6007     +290     
- Misses       2100     2134      +34     
- Partials      490      521      +31     

Files with missing lines	Coverage Δ
chainexchange/pubsub.go	78.07% <100.00%> (+15.79%)	⬆️
msg_encoding.go	53.84% <100.00%> (ø)
host.go	65.09% <54.54%> (-0.63%)	⬇️
partial_msg.go	81.81% <81.81%> (ø)
cbor_gen.go	28.76% <28.76%> (ø)

... and 7 files with indirect coverage changes