docs(tvix/nix-compat): rename as_narinfo() to to_narinfo()

This actually does a bit of allocation. There's two Vecs, one for
references and one for signatures.

We can get rid of the Vec at nar_hash.

Change-Id: Ie025309b6678f83f5b961d49ff75dcfc7da145a1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11395
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

tvix/store/src/proto/tests/pathinfo.rs

@@ -424,7 +424,7 @@ CA: fixed:sha256:086vqwk2wl8zfs47sq2xpjc9k066ilmb8z6dn0q6ymwjzlm196cd"#
     let path_info: PathInfo = (&narinfo_parsed).into();
 
     let mut narinfo_returned = path_info
-        .as_narinfo(
+        .to_narinfo(
             StorePathRef::from_bytes(b"pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz")
                 .expect("invalid storepath"),
         )