feat(flattenObject): add flattenObject for flatten object keys

[ngthuongdoan]

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[vercel]

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[ngthuongdoan]

Related #142

[raon0211]

Sorry for the late review. The implementation is a little bit hard for me to read. Please let me some time to add the review (Recently, a lot of pull requests and issues are springing up.)

[raon0211]

Hello, thanks for your pull request! I understand the needs for flattenObject.

Meanwhile, I think we have to implement flattenObject in an other way for these reasons:

• The current implementation uses lodash, which is what we prohibit, since using lodash from es-toolkit does not make sense.
• The current implementation is a bit complex to understand, while our core values of the library is simplicity.

Let me work on implementing flattenObject asap in another commit.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.53%. Comparing base (78c0c66) to head (cdcad81).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #183   +/-   ##
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  Coverage   99.52%   99.53%           
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  Files         105      106    +1     
  Lines         635      648   +13     
  Branches      123      128    +5     
=======================================
+ Hits          632      645   +13     
  Misses          3        3           

[raon0211]

Implemented flattenObject in this commit. Thanks for giving us ideas!

3e60443