Add config for progress bars

[nik-rev]

Description

This PR:

• Allows to customize the progress bar characters used via styles.widgets.progress_bar_chars
• Makes the progress bars more precise by using a larger range of unicode characters: ['▏', '▎', '▍', '▌', '▋', '▊', '▉', '█'], instead of |. This also makes them look smoother

Issue

None

Testing

• Run cargo test progress_bar
• Open with cargo run --basic and observe

Tested platforms:

• Windows
• _macOS
• _Linux (Arch Linux)
• _Other

Checklist

Ensure all of these are met:

• If this is a code change, areas your change affects have been linted using (cargo fmt)
• If this is a code change, your changes pass cargo clippy --all -- -D warnings
• If this is a code change, new tests were added if relevant
• If this is a code change, your changes pass cargo test
• The change has been tested to work (see above) and doesn't appear to break other things
• Documentation has been updated if needed (README.md, help menu, docs, configs, etc.)
• There are no merge conflicts
• You have reviewed the changes first
• The pull request passes the provided CI pipeline

[codecov]

Codecov Report

❌ Patch coverage is 64.63415% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.12%. Comparing base (9e2a675) to head (20c9e2b).
⚠️ Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
src/options/config/style/widgets.rs	37.93%	18 Missing ⚠️
src/canvas/widgets/mem_basic.rs	0.00%	5 Missing ⚠️
src/canvas/components/pipe_gauge.rs	90.24%	4 Missing ⚠️
src/canvas/widgets/cpu_basic.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1947      +/-   ##
==========================================
+ Coverage   54.00%   54.12%   +0.11%     
==========================================
  Files         120      121       +1     
  Lines       16565    16635      +70     
==========================================
+ Hits         8946     9003      +57     
- Misses       7619     7632      +13     

Flag	Coverage Δ
macos-14	46.81% <64.63%> (+0.13%)	⬆️
ubuntu-latest	52.54% <64.63%> (+0.12%)	⬆️
windows-2022	46.38% <65.43%> (+0.15%)	⬆️

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