Fix port cutting z position

[billingsley-john]

Proposed changes

This PR partially replaces #610 by implementing the z_pos - center_point changes to the port cutters. This PR does NOT add automatic port cutting to reactors (like #610) - this will be done in a separate PR

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactoring
• Documentation Update (if none of the other choices apply)
• New tests

Checklist

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• I have added tests that prove my fix is effective or that my feature works
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Further comments

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[shimwell]

Smaller PRs can be easier to merge in so thanks for this change. I shall take a look soon

[RemDelaporteMathurin]

Some really tiny comments :-)

[billingsley-john]

Thanks @RemDelaporteMathurin for the suggested changes

[codecov]

Codecov Report

Merging #714 (ce3bdf7) into develop (3208686) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #714   +/-   ##
========================================
  Coverage    98.87%   98.87%           
========================================
  Files           68       68           
  Lines         4337     4352   +15     
========================================
+ Hits          4288     4303   +15     
  Misses          49       49           

Impacted Files	Coverage Δ
...mak/parametric_components/port_cutters_circular.py	100.00% <100.00%> (ø)
.../parametric_components/port_cutters_rectangular.py	100.00% <100.00%> (ø)
paramak/parametric_shapes/extruded_mixed_shape.py	100.00% <100.00%> (ø)

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[billingsley-john]

Think this is ready to merge unless anyone has any suggestions? @RemDelaporteMathurin @shimwell

[billingsley-john]

Think this should be ready for merging @shimwell @RemDelaporteMathurin once tests pass