chore: add tests for slot binding

[baseballyama]

close: #564

I confirmed slot binding is works as expected in Svelte5 but not in Svelte4.
I just added tests for this.

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Latest commit: a69ee52

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[coveralls]

Pull Request Test Coverage Report for Build 12101386373

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 89.862%

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Totals
Change from base Build 12100948993:	0.0%
Covered Lines:	2998
Relevant Lines:	3217

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💛 - Coveralls