chore: add CODE_OF_CONDUCT.md

[ffforest]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

2. What is the scope of this PR (e.g. component or file name):

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

6. Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.90%. Comparing base (f5ea296) to head (d7c9d11).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #42   +/-   ##
=======================================
  Coverage   59.90%   59.90%           
=======================================
  Files           4        4           
  Lines        1100     1100           
=======================================
  Hits          659      659           
  Misses        339      339           
  Partials      102      102           

Flag	Coverage Δ
unittests	59.90% <ø> (ø)

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[liu-hm19]

lgtm