feat: expose HostMemoryOrVec via API

[theHamsta]

Since I needed the same primitive also for RustNN we could expose it in the trtx API. This helper is commonly when you either get owned engine bytes from TensorRT or from a cache.

[theHamsta]

This could also be

enum HostMemoryOrVec<'memory> {
    HostMemory(HostMemory<'memory>),
    Cow(Cow<'memory, [u8]>),
}

impl<'memory> AsRef<[u8]> for HostMemoryOrVec<'memory> {
    fn as_ref(&self) -> &[u8] {
        match self {
            HostMemoryOrVec::HostMemory(host_memory) => host_memory.as_ref(),
            HostMemoryOrVec::Cow(items) => items.as_ref(),
        }
    }
}

impl<'memory> Deref for HostMemoryOrVec<'memory> {
    type Target = [u8];

    fn deref(&self) -> &Self::Target {
        self.as_ref()
    }
}

impl<'buffer> From<HostMemory<'buffer>> for HostMemoryOrVec<'buffer> {
    fn from(value: HostMemory<'buffer>) -> Self {
        HostMemoryOrVec::HostMemory(value)
    }
}

impl<'memory> From<Cow<'memory, [u8]>> for HostMemoryOrVec<'memory> {
    fn from(value: Cow<'memory, [u8]>) -> Self {
        HostMemoryOrVec::Cow(value)
    }
}

so probably better leave to users to implement it themselves 🤷 ?

[mtavenrath]

Can you please update the PR using the Cow variant?

HostmMemoryOrVec is descriptive, but might not be true if this struct gets enhanced. Since HostMemory is already taken other potential names in the trtx namespace might be

Buffer
HostMemoryVariant
Bytes
BytesArray