use ref-cast for BlobRef cast

[skyzh]

https://github.com/dtolnay/ref-cast

Currently, we directly transmute these two types. We can use ref-cast crate to make it looks safer.

risinglight/src/types/blob.rs

Lines 99 to 104 in acb624c

	impl BlobRef {
	pub fn new(bytes: &[u8]) -> &Self {
	// SAFETY: `&BlobRef` and `&[u8]` have the same layout.
	unsafe { std::mem::transmute(bytes) }
	}
	}

[Kikkon]

can I have a try?

[skyzh]

Thanks! Please have a try.