fix: default OkHttpClient enhancements and testing

[Mohammad-Dwairi]

Situation

With the introduction of the new SDK core, we need to raise the tests coverage before attempting to migrate the core module to the original repository. We will be testing the new core with this LC SDK during this temporary phase.

We pushed the new core initially as an PoC. However, we are revising each module to cleanup, improve, and test.

Task

1. Cover all classes related to the default OkHttpClient in the new core with unit tests.
2. Improve and cleanup related classes where needed.

Action

Code Enhancements

1. Removed unneeded synchronization logic in BaseOkHttpClient that was used in the singleton pattern and relied on eager initialization of the default instance.
2. Moved all mapping logic between OkHttp and SDK Transport to extension functions.
3. Cleaned up OkHttpTransport implementation

Code Tests

1. Covered all classes in com.expediagroup.sdk.core.okhttp package with Kotlin tests and Java tests if needed.

Testing

All tests are passing

Results