feat: implement thorvg asset resolver for improved image handling

[tinyjin]

Replace existing base64 encoding pipeline with ThorVG's native asset resolver system.

This eliminates unnecessary encoding/decoding overhead and reduces memory usage when processing dotLottie image assets.

Asset Test Results

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[Copilot]

Pull Request Overview

This PR implements ThorVG's native asset resolver system to replace the existing base64 encoding pipeline for handling dotLottie image assets. This optimization eliminates unnecessary encoding/decoding overhead and reduces memory usage while maintaining the same functionality.

• Replace base64 encoding/decoding with direct asset resolution through ThorVG's native API
• Add asset resolver callback mechanism to handle image assets on-demand
• Remove redundant base64 encoding implementation and related constants

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
dotlottie-rs/src/lottie_renderer/thorvg.rs	Implements ThorVG asset resolver wrapper and integration with native API
dotlottie-rs/src/lottie_renderer/renderer.rs	Adds asset resolver trait method to Animation interface
dotlottie-rs/src/lottie_renderer/mod.rs	Defines AssetResolverFn type and adds asset resolver support to LottieRenderer trait
dotlottie-rs/src/fms/mod.rs	Replaces base64 encoding with direct asset resolution method
dotlottie-rs/src/dotlottie_player.rs	Integrates asset resolver callback with DotLottieManager for runtime asset loading

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[hermet]

This must be applied with ThorVG v1.0-pre30.

[tinyjin]

Fyi. @theashraf
While I prepare this patch, I had removed b64 encoding but just reverted it again, since dotLottie just introduced v2.0 Font Asset.

For now ThorVG doesn’t support Font Asset Resolver, this patch would cover the image asset resolution pipeline as this PR aims.

We’ll soon support Font with asset resolver and will separately make patch for the Font.

[tinyjin]

Some unit tests failed in CI/CD, but they pass consistently in my local environment.
The failed cases also appear unrelated to my changes, so I assume this is a temporary issue.
Please let me know if this patch actually broke the tests.

PR	Local