Clear out old instances from partial message management

[masih]

Once a decision about an instance is received, remove all states related to the older instances from partial message manager and chain exchange.

Part of #792

[codecov]

Codecov Report

Attention: Patch coverage is 47.05882% with 18 lines in your changes missing coverage. Please review.

Project coverage is 67.29%. Comparing base (2d636c9) to head (e48860b).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
partial_msg.go	21.73%	14 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #851      +/-   ##
==========================================
- Coverage   67.36%   67.29%   -0.07%     
==========================================
  Files          83       83              
  Lines        9024     9055      +31     
==========================================
+ Hits         6079     6094      +15     
- Misses       2410     2423      +13     
- Partials      535      538       +3     

Files with missing lines	Coverage Δ
chainexchange/pubsub.go	71.24% <100.00%> (+3.40%)	⬆️
host.go	66.05% <100.00%> (+0.28%)	⬆️
partial_msg.go	58.65% <21.73%> (-4.42%)	⬇️

... and 5 files with indirect coverage changes