feat(decoders): decode color baseline JPEGs in worker

[IbrahimCSAE]

Summary

• Add an OffscreenCanvas-based JPEG Baseline color decoder to the worker decoders.
• Route 8-bit color JPEGs through it so the full decode stays in the worker instead of bouncing back to the main thread
• Simplify the browser entry point since it no longer needs to pass a canvas down to the worker

That keeps the fast path but avoids running the browser decoder on the main thread for color JPEGs.

[IbrahimCSAE]

Might need to make this optional due to offscreen canvas support in browsers, will get to it.

[sedghi]

yes please make it optional default false