missing condition variable

Condition variable are missing from core synchronisation primitive. Only mutex and semaphore are present in mynewt.

Start by reviewing the existing core synchronization primitives, especially mutex and semaphore, to understand their APIs and integration points. Define the expected condition-variable behavior and scope before implementation. Done means condition variables are available as a core synchronization primitive alongside mutexes and semaphores, with appropriate validation from the project’s existing checks.

Written by the indexing model from the issue text.