substrate: Add basic file utility to read all the lines from a file

[amyspark]

Hey @dragonmux,

This is a PR to add a small line reader to Substrate.

As you'll find in the attached test suite, I wasn't able to make it work with UTF-16 and wchar_t strings. Hope you can assist me in that regard.

Let me know what you think 🐱

[dragonmux]

This is looking good - there are some stylistic items which we note below, and one query about something that seems missing, but we'll dig into this with you to understand the UTF-16 case and what's going on there

[dragonmux]

There's a couple of stylistic things to address, but this looks pretty close to mergable - nice work! ^_^

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (9f0886d) 89.24% compared to head (d12eac8) 89.27%.

Files	Patch %	Lines
substrate/file_utils	90.90%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #87      +/-   ##
==========================================
+ Coverage   89.24%   89.27%   +0.03%     
==========================================
  Files          47       48       +1     
  Lines        3516     3554      +38     
  Branches      688      703      +15     
==========================================
+ Hits         3138     3173      +35     
  Misses        341      341              
- Partials       37       40       +3     

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[dragonmux]

LGTM, we'll merge this once the builds complete. Thank you for the contribution!