feat: Add a loading state to the tagline image

[g123k]

Hi everyone!

The tagline image may take some time to load. This PR adds a loading state and some minor visual changes:  

➡️ As the SVG part is "your creation" @monsieurtanuki, please tell me if it's OK to add loadingBuilder and errorBuilder.

In terms of changes:

• svg_async_asset.dart: Add loadingBuilder and errorBuilder
• svg_cache.dart: Add loadingBuilder and errorBuilder
• svg_safe_network.dart: Add loadingBuilder and errorBuilder
• smooth_image.dart: The logo is moved to a dedicated file
• smooth_app_logo.dart: Exposes the 2 variants (animated and static)
• scan_tagline.dart: loading state + some minor changes (paddings essentially)
• app_icons.dart: Multiple constructors for CircledArrow + reordering classes alphabetically

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 3.03030% with 96 lines in your changes missing coverage. Please review.

Project coverage is 7.01%. Comparing base (4d9c7fc) to head (ed8c591). Report is 455 commits behind head on develop.

Files with missing lines	Patch %	Lines
...h_app/lib/generic_lib/widgets/smooth_app_logo.dart	4.34%	44 Missing :warning:
packages/smooth_app/lib/resources/app_icons.dart	4.16%	23 Missing :warning:
...ib/pages/scan/carousel/main_card/scan_tagline.dart	0.00%	16 Missing :warning:
...app/lib/cards/category_cards/svg_safe_network.dart	0.00%	6 Missing :warning:
..._app/lib/cards/category_cards/svg_async_asset.dart	0.00%	5 Missing :warning:
...smooth_app/lib/cards/category_cards/svg_cache.dart	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #5832 +/- ## ========================================== - Coverage 9.54% 7.01% -2.54% ========================================== Files 325 414 +89 Lines 16411 22539 +6128 ========================================== + Hits 1567 1581 +14 - Misses 14844 20958 +6114 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[teolemon]

thanks @g123k