@pragma('vm:entry-point') requirement for isolate entry points

[alnitak]

When spawning an isolate using Isolate.spawn(), the entry point callback function is invoked dynamically by the Dart VM. Unlike regular function calls that the compiler can track through static analysis, the VM looks up this function at runtime to start the isolate's execution.

This means that during tree-shaking (a process where the compiler removes unused code to reduce app size), the entry point function may be incorrectly identified as "dead code" and removed from the compiled output. This typically only manifests in release builds, causing the app to crash or fail silently when trying to spawn the isolate.

Solution

Add the @pragma('vm:entry-point') annotation to all isolate entry point functions.

Ref: pragmas

fixes #46

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