Slack/UI: Add wrapper around Slack conversations

[amotl]

About

For sending Slack messages directly through Python, instead of needing to pre-process or submit them otherwise.

Documentation: Slack UI

Details

• Available per CLI rapporto slack send.
• Includes proper formatting of standard Markdown content, as it seems to be a hassle, see Slack: Special message formatting #15.

Synopsis

rapporto slack send --channel=C08EF2NGZGB --message="**Hello, world.**"

[codecov]

Codecov Report

Attention: Patch coverage is 42.73504% with 134 lines in your changes missing coverage. Please review.

Project coverage is 62.51%. Comparing base (bc72097) to head (9d0dece).
Report is 60 commits behind head on main.

Files with missing lines	Patch %	Lines
src/rapporto/ui/slack.py	44.91%	65 Missing ⚠️
src/rapporto/util.py	30.61%	34 Missing ⚠️
src/rapporto/slack/cli.py	47.61%	33 Missing ⚠️
src/rapporto/github/model.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
- Coverage   68.25%   62.51%   -5.75%     
==========================================
  Files          14       15       +1     
  Lines         860     1083     +223     
==========================================
+ Hits          587      677      +90     
- Misses        273      406     +133     

Flag	Coverage Δ
unittests	62.51% <42.73%> (-5.75%)	⬇️

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