Auto merge of #26641 - dylni:fix-undefined-behavior, r=SimonSapin

Fix undefined behavior in `energymon::init`

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The layout of [`Box`](https://doc.rust-lang.org/std/boxed/struct.Box.html) is implicitly [`#[repr(Rust)]`](https://doc.rust-lang.org/nomicon/repr-rust.html), so it is undefined behavior to transmute it to another type. [`Box::into_raw`](https://doc.rust-lang.org/std/boxed/struct.Box.html#method.into_raw) can safely convert it to a pointer.

I did not run the test suite locally. I thought it would be better to let CI run than to set up the development environment for such a simple change. I did test that the file works individually with this change.

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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors

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- [X] These changes do not require tests because the undefined behavior is not visible

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