Metal shader pipeline states not released when compiled functions are erased

[robert-johansson]

When a compiled function is removed from CompilerCache (via compile_erase or compile_clear_cache), the associated Metal shader libraries and pipeline states in Device::library_kernels_ are not released. They persist until process exit.

Device::clear_library() exists but is never called from the compile cache cleanup path.

Found while investigating Metal resource accumulation in a long-running process that creates and discards compiled functions over time.

[robert-johansson]

CompilerCache::erase() (compile.cpp:370) removes the cache entry but never calls Device::clear_library() (device.h:165) for the kernel_lib_ names held by Compiled primitives in the tape. Same for CompilerCache::clear() at line 374. Device::library_kernels_ only grows.