fix: mpool: avoid deadlock on unsubscribe

[arajasek]

Related Issues

Fixes #7803

Proposed Changes

When unsubscribing all topics, pubsub will drain the subscription channel to avoid deadlocks. See
whyrusleeping/pubsub#1.

Also starts using https://github.com/filecoin-project/pubsub instead of https://github.com/whyrusleeping/pubsub

Checklist

Before you mark the PR ready for review, please make sure that:

• All commits have a clear commit message.
• The PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, INTERFACE BREAKING CHANGE, CONSENSUS BREAKING, build, chore, ci, docs,perf, refactor, revert, style, test
  • area: api, chain, state, vm, data transfer, market, mempool, message, block production, multisig, networking, paychan, proving, sealing, wallet, deps
• This PR has tests for new functionality or change in behaviour
• If new user-facing features are introduced, clear usage guidelines and / or documentation updates should be included in https://lotus.filecoin.io or Discussion Tutorials.
• CI is green

[codecov]

Codecov Report

Merging #8635 (9da58c5) into master (f22a0f9) will decrease coverage by 0.71%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #8635      +/-   ##
==========================================
- Coverage   40.81%   40.10%   -0.72%     
==========================================
  Files         686      686              
  Lines       75750    75750              
==========================================
- Hits        30920    30380     -540     
- Misses      39495    40092     +597     
+ Partials     5335     5278      -57     

Impacted Files	Coverage Δ
chain/store/store.go	64.83% <ø> (-0.67%)	⬇️
chain/messagepool/messagepool.go	63.65% <100.00%> (ø)
chain/sync.go	70.86% <100.00%> (ø)
extern/sector-storage/manager_post.go	5.97% <0.00%> (-76.12%)	⬇️
extern/sector-storage/sched_post.go	16.80% <0.00%> (-64.80%)	⬇️
cmd/lotus-worker/sealworker/rpc.go	0.00% <0.00%> (-36.00%)	⬇️
node/impl/remoteworker.go	0.00% <0.00%> (-33.34%)	⬇️
itests/kit/ensemble_opts_nv.go	76.00% <0.00%> (-24.00%)	⬇️
api/client/client.go	38.98% <0.00%> (-18.65%)	⬇️
itests/kit/node_opts.go	58.90% <0.00%> (-17.81%)	⬇️
... and 41 more