precommit: introduce `mdformat`

[Borda]

Why are these changes needed?

This is systematic solution to MD formatting as reported

Related issue number

for example, in #834

Checks

• [ ] I've included any doc changes needed for https://microsoft.github.io/FLAML/. See https://microsoft.github.io/FLAML/docs/Contribute#documentation to build and test documentation locally.
• [ ] I've added tests (if relevant) corresponding to the changes introduced in this PR.
• [ ] I've made sure all auto checks have passed.

[Borda]

the core change is 14fdf69, and the resulted formatting is in ac6f076

most of the changes are switch list syntax from * ... to - ...

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (550d1cf) 71.61% compared to head (a79e90a) 71.65%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1276      +/-   ##
==========================================
+ Coverage   71.61%   71.65%   +0.04%     
==========================================
  Files          83       83              
  Lines       11249    11249              
  Branches     2360     2360              
==========================================
+ Hits         8056     8061       +5     
+ Misses       2737     2734       -3     
+ Partials      456      454       -2     

Flag	Coverage Δ
unittests	71.53% <ø> (+0.04%)	:arrow_up:

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[Borda]

@sonichi @thinkall, mind check and share your opinion? :rabbit:

[Borda]

@sonichi @thinkall @jackgerrits, how are you doing? could you have a quick look? :flamingo:

[Borda]

@sonichi @jackgerrits, could you pls also have a look? :rabbit: