perf: intern cached str objects

[XuehaiPan]

Description

Describe your changes in detail.

Intern cached string literals to speed up Python internal dictionary lookup.

Checklist

Go over all the following points, and put an x in all the boxes that apply.
If you are unsure about any of these, don't hesitate to ask. We are here to help!

• I have read the CONTRIBUTION guide. (required)
• My change requires a change to the documentation.
• I have updated the tests accordingly. (required for a bug fix or a new feature)
• I have updated the documentation accordingly.
• I have reformatted the code using make format. (required)
• I have checked the code using make lint. (required)
• I have ensured make test pass. (required)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (abb03ab) 100.00% compared to head (16112fb) 100.00%.

❗ Current head 16112fb differs from pull request most recent head d4aef3d. Consider uploading reports for the commit d4aef3d to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #109   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          708       708           
=========================================
  Hits           708       708           

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.