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]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.07%. Comparing base (d67d3e1) to head (8e4cfbd).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #291      +/-   ##
==========================================
+ Coverage   65.94%   66.07%   +0.12%     
==========================================
  Files          78       78              
  Lines        5647     5647              
==========================================
+ Hits         3724     3731       +7     
+ Misses       1561     1556       -5     
+ Partials      362      360       -2     

Flag	Coverage Δ
unittests	66.07% <ø> (+0.12%)	⬆️

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[liu-hm19]

lgtm