refactor: somewhat migrate to Rust 2024 edition

[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:

This is just #1678, but without actually committing the edition/version to Cargo.toml.

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: Patch coverage is 49.15254% with 30 lines in your changes missing coverage. Please review.

Project coverage is 42.05%. Comparing base (9999a48) to head (1b4155f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/options/config/style/utils.rs	58.33%	10 Missing ⚠️
src/canvas/widgets/cpu_graph.rs	0.00%	6 Missing ⚠️
src/lib.rs	42.85%	4 Missing ⚠️
src/app/process_killer.rs	0.00%	2 Missing ⚠️
src/canvas/widgets/network_graph.rs	0.00%	2 Missing ⚠️
src/utils/general.rs	0.00%	2 Missing ⚠️
src/canvas.rs	0.00%	1 Missing ⚠️
src/collection/disks/unix/other/partition.rs	0.00%	1 Missing ⚠️
src/collection/disks/zfs_io_counters.rs	0.00%	1 Missing ⚠️
src/widgets/process_table/query.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1681       +/-   ##
===========================================
- Coverage   54.01%   42.05%   -11.97%     
===========================================
  Files         110      110               
  Lines       17503    17500        -3     
===========================================
- Hits         9454     7359     -2095     
- Misses       8049    10141     +2092     

Flag	Coverage Δ
macos-14	37.71% <46.55%> (+0.02%)	⬆️
ubuntu-latest	43.85% <47.27%> (-12.61%)	⬇️
windows-2019	37.60% <44.23%> (+0.01%)	⬆️

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