🧩 Finisher: Optimize cache cleaning and harden install checks

[tryigit]

Optimized gpu_cache_cleaner in Magisk Template/customize.sh to use find ... -exec ... + for significantly faster execution and better resource usage.
Hardened Android version check to handle empty getprop results gracefully, preventing syntax errors during installation.
Bumped module version to v1.0.4.
Added tests/verify.sh to verify script behavior and prevent regressions.

Verified by running tests/verify.sh which mocks the Magisk environment and confirms correct file deletion and error handling.

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PR created automatically by Jules for task 14365951348932015334 started by @tryigit

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