refactor: curp client propose

[bsbds]

This PR includes several changes:

• Moves client propose code to a seperate module propose_impl
• Improve propose latency for mutative commands
  This is done by simultaneously waitting for the record request to the cluster and the message from the leader gRPC stream.

Please briefly answer these questions:

• 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: Patch coverage is 83.12236% with 40 lines in your changes missing coverage. Please review.

Project coverage is 75.23%. Comparing base (e35b35a) to head (7cfccb6).
Report is 314 commits behind head on master.

Files with missing lines	Patch %	Lines
crates/curp/src/client/unary/propose_impl.rs	83.33%	24 Missing and 13 partials ⚠️
crates/curp/src/client/tests.rs	0.00%	2 Missing ⚠️
crates/curp/src/client/mod.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #975      +/-   ##
==========================================
- Coverage   75.55%   75.23%   -0.33%     
==========================================
  Files         180      190      +10     
  Lines       26938    28479    +1541     
  Branches    26938    28479    +1541     
==========================================
+ Hits        20353    21426    +1073     
- Misses       5366     5756     +390     
- Partials     1219     1297      +78     

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

[mergify]

@bsbds Your PR is in conflict and cannot be merged.

[mergify]

@bsbds Convert your pr to draft since CI failed