[Virtio-fs] [virtiofsd-rs] Issue closed: switch to using fuse-backend-rs

[virtiofs-bot at sinrega.org]

For clh, there is a crate [fuse-backend-rs](https://github.com/cloud-hypervisor/fuse-backend-rs) which provides core components like passthroughfs and fuse, including forget support and several corner case fixes around readdir (with [more](https://github.com/cloud-hypervisor/fuse-backend-rs/pull/10) to come)

By switching to it, virtiofsd-rs can not only get all fixes, but save a lot of code base.

Thoughts?
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https://gitlab.com/virtio-fs/virtiofsd-rs/-/issues/4