refactor: Unify chart popover state variables

[jperals]

Description

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov[bot]]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (61deb3a) 94.63% compared to head (b376109) 94.63%. Report is 1 commits behind head on main.

Files	Patch %	Lines
src/mixed-line-bar-chart/chart-container.tsx	76.92%	3 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1819   +/-   ##
=======================================
  Coverage   94.63%   94.63%           
=======================================
  Files         654      653    -1     
  Lines       17787    17778    -9     
  Branches     5861     5865    +4     
=======================================
- Hits        16833    16825    -8     
+ Misses        887      886    -1     
  Partials       67       67           

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