feat: automatic load pages in animated images

[STRRL]

close #229

references:

• Support animated images davidbyttow/govips#117
• Animated GIF support davidbyttow/govips#246

[STRRL]

Hi @n0vad3v PTAL ❤️

[codecov]

Codecov Report

Merging #231 (15418f9) into master (9efead2) will decrease coverage by 3.15%.
The diff coverage is 78.05%.

@@            Coverage Diff             @@
##           master     #231      +/-   ##
==========================================
- Coverage   83.57%   80.43%   -3.15%     
==========================================
  Files           6        6              
  Lines         542      639      +97     
==========================================
+ Hits          453      514      +61     
- Misses         61       85      +24     
- Partials       28       40      +12     

Impacted Files	Coverage Δ
encoder.go	67.56% <69.56%> (-9.58%)	⬇️
helper.go	82.35% <74.60%> (-6.42%)	⬇️
router.go	93.16% <95.00%> (+3.47%)	⬆️
config.go	100.00% <100.00%> (ø)
prefetch.go	100.00% <100.00%> (ø)
webp-server.go	79.20% <100.00%> (+2.03%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more