fix: provide theme to SvgAssetLoader instead of SvgPicture

[Kirpal]

What does this change?

Since version 5.5.0+1, the SvgTheme no longer works. It doesn't work because flutter_svg has deprecated using the theme with the SvgPicture constructor, and suggests that you pass the theme to the bytes loader instead.

Fixes #531 🎯

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Checklist:

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• [x] Make sure to open a GitHub issue as a bug/feature request before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
  • [x] Ensure the tests (melos run test)
  • [x] Ensure the analyzer and formatter pass (melos run format to automatically apply formatting)
• [x] Appropriate docs were updated (if necessary)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.27%. Comparing base (dbc01db) to head (b427a82).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #532 +/- ## ======================================= Coverage 97.27% 97.27% ======================================= Files 22 22 Lines 772 772 ======================================= Hits 751 751 Misses 21 21 ```

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