Add test coverage for validateDateRange function

[coderabbitai]

Description

The newly implemented validateDateRange function in src/device-registry/validators/activities.validators.js lacks test coverage. This function is critical as it validates that activity dates are not in the future and not more than one month in the past.

Requirements

Please add unit tests that verify:

• A date in the future correctly triggers an error.
• A date more than one month in the past correctly triggers an error.
• A valid date within the acceptable range returns true.

Context

• Referenced in PR: Fix: Implement Date Range Validation for Activity Dates #4515
• Comment URL: Fix: Implement Date Range Validation for Activity Dates #4515 (comment)

Importance

Adding these tests will help ensure robust edge-case handling and maintain code quality as the application evolves.

Acceptance Criteria

• Unit tests created for the validateDateRange function
• All test cases passing
• Code coverage for the function reaches 100%