fix(utils): prevent prototype pollution in deepExtend

[lahirumaramba]

Prevent prototype pollution in deepExtend

[gemini-code-assist]

Code Review

This pull request adds a security check to the deepExtend function in src/utils/deep-copy.ts to prevent prototype pollution by skipping __proto__, constructor, and prototype properties. The feedback suggests adding unit tests to verify that these prototype pollution vectors are successfully blocked and to prevent future regressions.

[gemini-code-assist]

While the prototype pollution check is correct, there are no unit tests included in this pull request to verify that deepExtend successfully blocks prototype pollution attempts (e.g., using __proto__, constructor, or prototype). Adding unit tests for these edge cases is highly recommended to prevent future regressions. For example, you can add tests like:\n\ndescribe('deepExtend prototype pollution', () => {\n it('should not pollute prototype via proto', () => {\n const payload = JSON.parse('{"proto": {"polluted": true}}');\n deepExtend({}, payload);\n expect((Object.prototype as any).polluted).to.be.undefined;\n });\n\n it('should not pollute prototype via constructor', () => {\n const payload = JSON.parse('{"constructor": {"prototype": {"polluted": true}}}');\n deepExtend({}, payload);\n expect((Object.prototype as any).polluted).to.be.undefined;\n });\n});