feat: implement style api for progress bar component

[mxschll]

Description

Extends the progress bar component with a style API for customization, allowing developers to override default component styles.

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

How has this been tested?

• Added unit tests for style prop validation and CSS class application
• Screenshot tests passed without visual regressions

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]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.25%. Comparing base (7790068) to head (1720cd4).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4022   +/-   ##
=======================================
  Coverage   97.25%   97.25%           
=======================================
  Files         859      860    +1     
  Lines       25400    25432   +32     
  Branches     9050     9064   +14     
=======================================
+ Hits        24703    24735   +32     
  Misses        650      650           
  Partials       47       47           

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