Flow sign in the pipe component

[nabily-met]

Goal

Replaced Q^2 by Q*abs(Q) in the Pipe component to have a unique flow direction according the pressure difference we have on the pipe.

Closes #384

Type of change

• Bugfix
• New feature
• Refactoring change
• Release & Version Update (don't forget to change the version number in package.mo)

Will it break anything in previous models ?

• Breaking change (If yes, make sure to point it out in the changelog)
• Non-Breaking change

Checklist

• I have added the appropriate tags, reviewers, projects (and detailed the size and priority of my PR) and linked issues to this PR
• I have performed a self-review of my own code
• I have checked that all existing tests pass.
• I have added/updated tests that prove my development works and does not break anything.
• I have made corresponding changes or additions to the documentation (in Notion documentation)
• I have added corresponding entries to the Changelog
• I have checked for conflicts with target branch, and merged/rebased in consequence

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