Extract realpath before computing relative path in symlink_force

[jinmannwong]

Description

Incorrect relative path can be computed when one of the paths is itself a link as raised in #33. This PR addresses this issue by extracting the realpath first before computing the relative path.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

@@            Coverage Diff             @@
##             develop      #34   +/-   ##
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  Coverage           ?   40.67%           
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  Files              ?       48           
  Lines              ?    10157           
  Branches           ?        0           
==========================================
  Hits               ?     4131           
  Misses             ?     6026           
  Partials           ?        0           

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