Smart settle

[Guillembonet]

Closes: #5067

Current problems:

• We settle at 5 MYST always and maybe fees are huge when we do, it's a matter of luck.
• We call transactor /fee endpoint a lot. In the last 3 minutes there are 1400 calls yet coming only from 550 different nodes.

Proposed solutions:

• Automatic settlements will be smarter now and work as follows:
  • We have 3 values: minimum to settle(5), max fee percentage(5%), and max unsettled(20)
  • If unsettled is below minimum we don't settle
  • If unsettled is above the maximum we always auto-settle
  • If it's somewhere in between we automatically settle if the transaction fees are less than the percentage (i.e. if we have 6 MYST unsettled we will settle as long as the fees are less than 0.3 MYST)
• Transactor fees are now cached for 3 minutes 30 seconds (by default) instead of calling every time. Keep in mind that the smart settlement check requires a call there on every hermes promise received (only if we have more unsettled than 5), so with both changes, we might still call transactor /fee endpoint quite a lot but I think it should be less. We can discuss whether we should increase this cache amount a bit more (more than 10 mins will for sure be bad).

Signed-off-by: Guillem Bonet guillem@mysterium.network

[codecov-commenter]

Codecov Report

Merging #5113 (2df76f7) into master (cdaa020) will decrease coverage by 0.08%.
The diff coverage is 29.11%.

@@            Coverage Diff             @@
##           master    #5113      +/-   ##
==========================================
- Coverage   39.11%   39.03%   -0.09%     
==========================================
  Files         359      359              
  Lines       19155    19208      +53     
==========================================
+ Hits         7493     7497       +4     
- Misses      10927    10973      +46     
- Partials      735      738       +3     

Impacted Files	Coverage Δ
config/flags_payments.go	0.00% <0.00%> (ø)
config/flags_transactor.go	0.00% <0.00%> (ø)
core/node/options.go	0.00% <0.00%> (ø)
identity/registry/transactor.go	0.00% <0.00%> (ø)
mobile/mysterium/entrypoint.go	0.00% <0.00%> (ø)
session/pingpong/hermes_promise_settler.go	34.60% <76.66%> (+1.17%)	⬆️
requests/dialer_swarm.go	73.68% <0.00%> (-2.26%)	⬇️
tequilapi/endpoints/sse_handler.go	70.00% <0.00%> (-2.15%)	⬇️
nat/traversal/pinger.go	74.80% <0.00%> (-1.94%)	⬇️
... and 1 more

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[tomasmik]

I would probably just remove the cache, but it's fine either way.