Consolidate runtime teardown fix onto rust feature/platform-audio-stability

Point the submodule at rust-sdks feature/platform-audio-stability
(fd48e5c2) instead of feature/platform-audio-runtime-teardown
(7283a3bc). The stability branch carries the same fixes - audio I/O
stop-before-detach ordering in AdmProxy and the LkRuntime teardown
gate - with one strengthening: the teardown gate is released by a
guard declared as the last LkRuntime field, so it only opens after
the peer connection factory (and its ADM/worker threads) has been
fully destroyed, rather than at the start of Drop before the factory
field is torn down.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: alan-george-lk