chore: make cached JNI static handles const

[mrousavy]

Motivation

• Cached JNI method/field handles and generated constructor lookups were declared as mutable static auto, which is unnecessary and risks accidental mutation.
• Making these cached handles static const auto improves correctness and allows the compiler to place them in read-only memory.

Description

• Updated the Nitrogen codegen template in packages/nitrogen/src/syntax/kotlin/KotlinHybridObjectRegistration.ts to emit static const auto constructorFn for hybrid-object registration stubs.
• Changed runtime JNI cached lookups from static auto to static const auto in packages/react-native-nitro-modules/android/src/main/cpp/core/JHybridObject.cpp and packages/react-native-nitro-modules/android/src/main/cpp/utils/JThreadUtils.hpp.
• Updated generated Android on-load sources in the test packages packages/react-native-nitro-test/nitrogen/generated/android/NitroTestOnLoad.cpp and packages/react-native-nitro-test-external/nitrogen/generated/android/NitroTestExternalOnLoad.cpp to match the new codegen output.

Testing

• Ran bun run build, which executes the project build and codegen for all packages, and the command completed successfully.

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Codex Task

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
nitro-docs	Skipped		Mar 6, 2026 10:40am