refactor: simplify temperature conversion function usage

[ClementTsang]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

Just make it a function on the temperature type enum.

Issue

If applicable, what issue does this address?

Closes: #

Testing

If relevant, please state how this was tested. All changes must be tested to work:

If this is a code change, please also indicate which platforms were tested:

• Windows
• macOS
• Linux

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (10a37c2) 31.57% compared to head (49c1604) 31.68%.

Files	Patch %	Lines
src/app/data_harvester/temperature/linux.rs	0.00%	4 Missing ⚠️
src/app/data_harvester/nvidia.rs	0.00%	2 Missing ⚠️
src/app/data_harvester/temperature.rs	95.23%	1 Missing ⚠️
src/app/data_harvester/temperature/sysinfo.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1326      +/-   ##
==========================================
+ Coverage   31.57%   31.68%   +0.11%     
==========================================
  Files          97       97              
  Lines       16943    16953      +10     
==========================================
+ Hits         5349     5372      +23     
+ Misses      11594    11581      -13     

Flag	Coverage Δ
macos-12	33.45% <83.33%> (+0.12%)	⬆️
ubuntu-latest	33.26% <74.07%> (+0.11%)	⬆️
windows-2019	33.49% <83.33%> (+0.12%)	⬆️

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