refactor: move device resource and datasource to separate package

[ctreatma]

This moves the device resource and data sources out of the equinix package and into an isolated directory & package to align with #106.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 80.95238% with 16 lines in your changes missing coverage. Please review.

Project coverage is 51.89%. Comparing base (f8c2ab9) to head (d698e10).
Report is 9 commits behind head on main.

Files	Patch %	Lines
internal/resources/metal/device/resource.go	84.09%	6 Missing and 1 partial ⚠️
internal/resources/metal/device/datasource.go	83.87%	4 Missing and 1 partial ⚠️
internal/resources/metal/device/sweeper.go	0.00%	3 Missing ⚠️
internal/resources/metal/device/helpers.go	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##             main     #707       +/-   ##
===========================================
+ Coverage   34.44%   51.89%   +17.45%     
===========================================
  Files         151      152        +1     
  Lines       20710    20922      +212     
===========================================
+ Hits         7133    10857     +3724     
+ Misses      13415     9630     -3785     
- Partials      162      435      +273     

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