fix(@toss/utils) added improvements and test code to the queryString function.

[Gaic4o]

Overview

Hello. While modifying the query String function, I organized it into docs, fixes, and test formats.

docs: Translated existing comments and test code within queryString.spec.ts, queryString.ts from Korean to English.

Fix: Refactored the test case to use the QS module instead of calling the function directly. These changes will ensure that test cases more closely match real-world usage patterns when used in production in the QS modular format.

Test: We improved coverage by adding test cases for QS.get.

• [x] I read and included theses actions below

1. I have read the Contributing Guide
2. I have written documents and tests, if needed.

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