refactor: some optimizations for linux data collection

[ClementTsang]

Description

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Issue

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Closes: #

Testing

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

• [ ] Windows
• [ ] macOS
• [x] Linux

Checklist

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• [ ] 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[bot]]

Codecov Report

:x: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 36.77%. Comparing base (f1017d6) to head (73edcd9). :warning: Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/collection.rs	0.00%	3 Missing :warning:
src/collection/processes/unix/process_ext.rs	0.00%	1 Missing :warning:
src/collection/processes/unix/user_table.rs	0.00%	1 Missing :warning:

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HEAD has 1 upload less than BASE

Flag	BASE (f1017d6)	HEAD (73edcd9)
ubuntu-latest	1	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1807      +/-   ##
==========================================
- Coverage   42.12%   36.77%   -5.35%     
==========================================
  Files         115      107       -8     
  Lines       16215    14971    -1244     
==========================================
- Hits         6830     5506    -1324     
- Misses       9385     9465      +80     

Flag	Coverage Δ
macos-14	37.35% <0.00%> (-0.01%)	:arrow_down:
ubuntu-latest	?
windows-2022	37.69% <0.00%> (-0.02%)	:arrow_down:

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[ClementTsang]

The bug fix is needed, but iffy on the read_link stuff.

[ClementTsang]

(as the slow part seems to be with the readlink itself no matter what)