Image optimization on the fly (for JPEG/PNG/WebP)

[satyamtg]

This adds image optimization on the fly for JPEG/WebP and PNG files. GIFs are not supported as I wasn't able to achieve any better compression than the original file in most of my tests using Pillow. Using gifsicle would mean not doing it "on the fly"

Here's a list of major changes -

• The methods optimize_jpeg() and optimize_png() now use the methods from optimize_images directly for processing the image in different stages rather than making a Task and using optimize_images task for that. This has several benefits -

  • It allows better control over how the image is processed
  • No need to pass unnecessary constants
  • It was necessary for the "on the fly" version as the task-based approach in optimize_images() would rewrite the file on the disk. it assumes that you are NOT passing anything other than a path. So we now can give a image as a byte stream, and save it as a file and vice versa too

• Unnecessary functions like run_optimize_images_task() and create_temporary_file() are now removed

• The return value now also contains the path of the destination or the BytesIO object that contains the optimized image

Todo -

• 100% coverage (Add tests for grayscale and some minor stuff. Maybe grayscale can be removed. What do you say @kelson42 , @rgaudin )
• Adaptation of the entire image module for on the fly operation - That will require changes in transformation and conversion functions too. But probably, that can be better managed outside this PR

[codecov[bot]]

Codecov Report

Merging #75 (91bd685) into master (b895fc7) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #75   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           25        25           
  Lines          997      1007   +10     
=========================================
+ Hits           997      1007   +10     

Impacted Files	Coverage Δ
src/zimscraperlib/image/optimization.py	100.00% <100.00%> (ø)
src/zimscraperlib/image/probing.py	100.00% <100.00%> (ø)

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