chore(deps): add @std/assert explicitly

[Yusuke4869]

No description provided.

[Copilot]

Pull Request Overview

This PR adds an explicit import mapping for @std/assert in the Deno configuration and updates all test files to use the mapped import path instead of the direct JSR URL.

• Added @std/assert import mapping to deno.json
• Updated test file imports to use the mapped path @std/assert instead of jsr:@std/assert

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

File	Description
deno.json	Added explicit import mapping for @std/assert package
src/usecase/item/impl.test.ts	Updated import to use mapped path
src/repository/item/impl.test.ts	Updated import to use mapped path
src/domain/item/impl.test.ts	Updated import to use mapped path

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