A couple of small fixes for unit types

[alexdewar]

Description

I was fiddling with unit types on another branch and noticed a couple of small problems:

1. A unit type U divided by U should yield Dimensionless, not U
2. We should pass self by ref (&self) not value (self) for various methods of unit types, otherwise it'll be consumed when they're run

Type of change

• Bug fix (non-breaking change to fix an issue)
• New feature (non-breaking change to add functionality)
• Refactoring (non-breaking, non-functional change to improve maintainability)
• Optimization (non-breaking change to speed up the code)
• Breaking change (whatever its nature)
• Documentation (improve or add documentation)

Key checklist

• All tests pass: $ cargo test
• The documentation builds and looks OK: $ cargo doc

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[Copilot]

Pull Request Overview

This PR fixes issues with unit types by updating the division operator to return a Dimensionless type and modifying methods to take self by reference instead of by value.

• Update division operator to yield Dimensionless
• Change method signatures (value, is_normal, is_finite, abs) to use &self

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.43%. Comparing base (f6ff308) to head (86791a4).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #654   +/-   ##
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  Coverage   88.43%   88.43%           
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  Files          39       39           
  Lines        3555     3555           
  Branches     3555     3555           
=======================================
  Hits         3144     3144           
  Misses        219      219           
  Partials      192      192           

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[tsmbland]

1. A unit type U divided by U should yield Dimensionless, not U

Silly me 🤦