fix(sdk): harden model lifecycle and Xray validation

[Kristoffer Södersten (kristoffersodersten)]

Summary

• serialize Android LLM/VLM handle operations and make stop/destroy lifecycle safe
• reject invalid native handles and release llama.cpp VLM sampler/model resources
• select GenieX QAIRT assets consistently in the model manager
• add a versioned, fail-closed Xray full-lap contract with focused regression tests

Why

The Android demo needs deterministic cleanup, causal validation, and workload-level evidence instead of relying on short peak throughput measurements. These changes address native handle races and resource residue while establishing the initial lightweight/deep Xray measurement contract.

Validation

• C++17 Xray contract tests passed in an NDEBUG build
• Xray contract tests passed with UBSan
• git diff --check passed
• focused Rust selector tests could not link in the current Android/Termux environment because host linker libraries liblog and libunwind were unavailable
• ASan could not reserve its shadow address space under Termux/proot; this occurred before test execution

Scope

This is the reviewed Patch 1 and lifecycle correction set. It does not begin Patch 2 or claim production/device endurance completion.