fix: Set SpriteButtonComponent sprites in `onMount`

[spydon]

Description

Since it will be confusing for the user to have to call super.onLoad last when they override onLoad, we move setting the sprites to onMount.

Checklist

• [x] I have followed the Contributor Guide when preparing my PR.
• [x] I have updated/added tests for ALL new/updated/fixed functionality.
• [x] I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• [x] I have updated/added relevant examples in examples or docs.

Breaking Change?

• [x] No, this PR is not a breaking change.

Related Issues

[spydon]

@puneet-739 now it should be fixed, I didn't have the time to properly test it last time since I wasn't home, but now I was. If you want to test it you can depend on this branch in your project, or main once it is merged.

[puneet-739]

@puneet-739 now it should be fixed, I didn't have the time to properly test it last time since I wasn't home, but now I was. If you want to test it you can depend on this branch in your project, or main once it is merged.

@spydon everything is working perfectly now! : )