Remove buffer as peer dependency

[limemloh]

Description

When using the SDK, the user will need to install buffer as a dependency, since types from this library is exposed in the public API of our SDK.
Currently, we don't list it as a peerDependency in package.json and we could fix that, but IMO it would be more appropriate to only expose ArrayBuffer and only use buffer internally.

[soerenbf]

I agree. We can still resolve to the browser-specific implementation in the web target, but it does feel awkward to have to use "our" version of buffer even in the node SDK, when the platform has it as a native type as well (and if you use the native type with typescript, you get type errors).