Add learner

[themanforfree]

Please briefly answer these questions:
#306

• what problem are you trying to solve? (or if there's no problem, what's the motivation for this change?)

• what changes does this pull request make?

• are there any non-obvious implications of these changes? (does it break compatibility with previous versions, etc)

[codecov]

Codecov Report

Attention: 73 lines in your changes are missing coverage. Please review.

Comparison is base (601c710) 52.77% compared to head (4e2677e) 52.87%.
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #449      +/-   ##
==========================================
+ Coverage   52.77%   52.87%   +0.10%     
==========================================
  Files         104      104              
  Lines       18156    18275     +119     
  Branches    18156    18275     +119     
==========================================
+ Hits         9581     9663      +82     
- Misses       8007     8035      +28     
- Partials      568      577       +9     

Files	Coverage Δ
curp-test-utils/src/test_cmd.rs	77.81% <ø> (ø)
curp/src/server/raw_curp/tests.rs	73.93% <97.14%> (+1.70%)	⬆️
curp/src/rpc/mod.rs	25.16% <63.63%> (+3.95%)	⬆️
curp/src/members.rs	81.67% <42.85%> (-1.94%)	⬇️
curp/src/server/raw_curp/state.rs	91.08% <83.33%> (-2.78%)	⬇️
curp/src/server/curp_node.rs	15.35% <8.33%> (-0.09%)	⬇️
curp/src/server/raw_curp/mod.rs	68.07% <71.42%> (-0.87%)	⬇️

... and 4 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Phoenix500526]

LGTM