TDL-20359 Add custom exception handling.

[prijendev]

Description of change

• Added custom exception class for each error code.
• Added backoff logic to retry all 5xx errors, TimeoutError and ConnnectionError.
• Set default timeout of 6 seconds as per documentation.
• Added request timeout.
• Skip 404 error for time_entries stream.
• Added unit tests to verify error messages and retry counts.

Manual QA steps

Risks

Rollback steps

• revert this branch