Throw if using secret key

[cameron-morrow-toptal]

copy of radarlabs/radar-sdk-ios#465

[Copilot]

Pull Request Overview

This PR adds validation to prevent the use of secret keys during Radar SDK initialization. The change ensures that only publishable keys are accepted by throwing an IllegalArgumentException when a secret key (containing "sk") is provided.

Key changes:

• Added secret key validation in the Radar.initialize() method
• Added comprehensive test coverage for the new validation logic

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
sdk/src/main/java/io/radar/sdk/Radar.kt	Added validation to throw exception when secret key is detected
sdk/src/test/java/io/radar/sdk/RadarTest.kt	Added test cases to verify secret key validation and exception handling

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