fix: allow Raw as UnixfsType

[ramfox]

Acknowledges that a raw node is a valid UnixfsNode and therefore can be resolved as a file in the gateway

closes n0-computer/beetle#148

[Arqu]

nice

[dignifiedquire]

@ramfox I don't think this is quite correct. IPLD Raw is something else than Unixfs Raw. We shouldn't treat them the same.

Asfaiu the current kubo gateway allows unixfs paths -> other ipld blocks which is likely why it works on their side. If we start allowing for that we should explicitly resolve IPLD, not treat IPLD as unixfs

[ramfox]

Okay great, thank you. I had a feeling this was off so I wrote up an alternative way of doing this here. But I'm also woefully ignorant of the way the gateway should ideally operate.

Before this PR, the path to get to the bug was this:
The request comes in.
The get_handler determines that the ResponseFormat is ResponseFormat::Fs (most likely because this seems to be a kind of default).
The get_handler matches on the response format & calls serve_fs, which errors when the unixfs_type of the resolved node is found to be None (hence the "couldn't determine unixfs type" error).

So the problem is either:

1. we are incorrectly assuming that the response format should be ResponseFormat::Fs, and instead should be ResponseFormat::Raw. Fixing the ResponseFormat type, would call serve_raw rather than serve_fs. Problem solved? (@Arqu ???)
2. serve_fs should actually just be able to handle OutType::Raw (the above-linked solution). We handle OutType::Raw & the problem is solved.
3. There is some alternative way we should be handling raw blocks that we don't have set up yet that I need clarity on

[Arqu]

1. we are incorrectly assuming that the response format should be `ResponseFormat::Fs`, and instead should be `ResponseFormat::Raw`. Fixing the `ResponseFormat` type, would call `serve_raw` rather than `serve_fs`. Problem solved? (@Arqu ???)

Technically the ResponseFormat is correct and line by line is pretty much also what kubo does. Where we seem to differ is that we don't handle the calls well so we potentially want to diverge and redirect that.

Not sure whether we can correctly "detect" this state, but given we can return OutType::Raw as the body we can just make a special case next to dir and file handling.

[ramfox]

@Arqu something like this?: #332