✨ Add metadata when encoding

[inflation]

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[codecov]

Codecov Report

Attention: Patch coverage is 78.04878% with 18 lines in your changes are missing coverage. Please review.

Project coverage is 96.58%. Comparing base (1fe7130) to head (4477972).

Files	Patch %	Lines
jpegxl-rs/src/encode.rs	11.76%	15 Missing ⚠️
jpegxl-rs/src/encode/metadata.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #49      +/-   ##
==========================================
- Coverage   98.71%   96.58%   -2.14%     
==========================================
  Files          12       15       +3     
  Lines         858      879      +21     
==========================================
+ Hits          847      849       +2     
- Misses         11       30      +19     

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