refactor: hide egl code behind feature in libwayshot

[Gigas002]

This PR hides egl-related code in libwayshot behind feature (enabled by default).
This may seem useless at the moment, but this is part of further refactoring before implementing optional vulkan support. I've been testing and using it in my fork for ~2 weeks and things are looking good.

Breaking changes

While this is not breaking for most users, default-features = false users will lose egl support. Migration step is to add feature, e.g. libwayshot = { version = "...", default-features = false, features = ["png", "egl"] }.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 91 lines in your changes missing coverage. Please review.
✅ Project coverage is 17.66%. Comparing base (0e3e91f) to head (270cde1).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
libwayshot/src/egl.rs	0.00%	80 Missing ⚠️
libwayshot/src/lib.rs	0.00%	6 Missing ⚠️
libwayshot/src/screencast.rs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #320      +/-   ##
==========================================
+ Coverage   17.63%   17.66%   +0.02%     
==========================================
  Files          19       20       +1     
  Lines        2988     2983       -5     
==========================================
  Hits          527      527              
+ Misses       2461     2456       -5     

Flag	Coverage Δ
libwayshot	22.24% <0.00%> (+0.04%)	⬆️
wayshot	0.00% <ø> (ø)

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[Gigas002]

Hmm, probably we don't even need it as default feature in cli...

[Decodetalkers]

oh.. sorry, this is just a draft. I should not approve it now

[Gigas002]

Yeah, my bad. I've opened it yesterday, but now I thought that maybe we don't need that feature on by default in cli, since we don't use egl on it to capture screenshot anyway

[Gigas002]

@Decodetalkers
Sorry, I've removed the egl feat from wayshot cli. Can you please re-review when you're free?
Thank you!