fix(resizer): guard dispose() against an in-flight resize()

[jslok]

Split out of #4117 (as requested).

resize() null-checks _pipeline and then dereferences it with no synchronization, while dispose() can concurrently reset the same unique_ptr from the JS thread — running ~VulkanResizerPipeline() and tearing down the VkDevice under an in-flight run(). That is a native use-after-free instead of the catchable "already been disposed" error. iOS has the same shape: an unguarded pipeline = nil racing the guard let load is a data race on the possibly-last reference.

Fix: serialize resize(), dispose() and the memorySize getter behind a lifecycle lock (std::mutex / NSLock). A dispose landing mid-frame blocks until that resize returns; every later call throws the catchable error. The getter is included because Nitro reads it from toObject() on arbitrary threads; it is never called from inside resize()/dispose(), so it cannot self-deadlock.

Tested on device on both platforms: on Android by disposing from an effect cleanup while frames were still being processed, and on iOS where this change has been shipping in our production app as a patch-package patch.

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