test: latency of internal payments within fed

[okjodom]

Adds latency test coverage to transactions between two fedimint clients in a federation.
From initial tests, turns out these internal transactions are currently much slower than LN sends / receives!
A follow up here is to investigate and improve internal payments perf

================= RESULTS ==================
REISSUE: min: 1.7s, avg: 1.8s, median: 1.8s, p90: 1.9s, max: 2.0s, sum: 54.1s
LN SEND: min: 2.9s, avg: 3.1s, median: 3.1s, p90: 3.2s, max: 4.4s, sum: 62.8s
LN RECV: min: 1.9s, avg: 2.2s, median: 2.2s, p90: 3.0s, max: 3.1s, sum: 44.1s

FM PAY: min: 4.2s, avg: 4.7s, median: 4.4s, p90: 5.0s, max: 9.4s, sum: 93.5s

closes #3695

[codecov]

Codecov Report

Attention: 39 lines in your changes are missing coverage. Please review.

Comparison is base (bc4ccf5) 57.08% compared to head (5761793) 56.95%.

Files	Patch %	Lines
devimint/src/main.rs	0.00%	32 Missing ⚠️
devimint/src/federation.rs	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3964      +/-   ##
==========================================
- Coverage   57.08%   56.95%   -0.14%     
==========================================
  Files         193      193              
  Lines       43043    43078      +35     
==========================================
- Hits        24572    24533      -39     
- Misses      18471    18545      +74     

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[elsirion]

Looks good :)

[justinmoon]

Nice. @okjodom could you make an issue for the investigation?