fix: use try_into instead of as u64 cast in push_buffer

[JM00NJ]

Follow-up to #1820.

Replaces as u64 cast with .try_into() in push_buffer for correctness and future-proofing, as suggested by @jprendes. While usize == u64 on both x86_64 and ARM64 currently, .try_into() makes the conversion explicit and safe for any future platform changes.

[jprendes]

Thanks @JM00NJ !

[jprendes]

@JM00NJ could you add the sign-off line to the commits message? The DCO check is failing. Thanks!

[andreiltd]

Hey @JM00NJ, thanks for the fixes! I just wanted to give you a heads-up about the stack communication, that it will be soon replaced by virtual queue based comms. This means that, unfortunately, the changes from this PR and push_buffer PR will not make to the next release just because they are applied on soon to-be-wiped code.

[JM00NJ]

Hey @JM00NJ, thanks for the fixes! I just wanted to give you a heads-up about the stack communication, that it will be soon replaced by virtual queue based comms. This means that, unfortunately, the changes from this PR and push_buffer PR will not make to the next release just because they are applied on soon to-be-wiped code.

Thanks for the heads up! Good to know about the virtual queue migration. I'll take a look at #1794 ; happy to contribute there once the new implementation lands.

[jprendes]

Also, the commit also needs to be GPG signed, I'm happy to merge it after you sign it, even if this code is going away.