[executorch][android] Add Runtime.java to centralize native library l…

[LefterisXefteris]

This pull request addresses #10439 by introducing a Runtime.java class to centralize the loading of the native libexecutorch.so library on Android.

What’s Included
• Added Runtime.java in org.pytorch.executorch with a static loader block
• Updated NativePeer.java and LlmModule.java to defer initialization to Runtime.isInitialized()
• Added RuntimeTest.java to verify proper initialization

[pytorch-bot]

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