feat(tvix/nix-compat): add narinfo::Signature::verify

This adds support for verifying signatures found in NARInfo files.

This still needs to be hooked together with the nix+http[s] backend.

Change-Id: Ic1c8ddbdecfb05cefca2492808388b0f7f3f2637
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10081
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

tvix/nix-compat/Cargo.toml

@@ -12,6 +12,8 @@ async = ["futures-util"]
 bitflags = "2.4.1"
 bstr = { version = "1.6.0", features = ["alloc", "unicode", "serde"] }
 data-encoding = "2.3.3"
+ed25519 = "2.2.3"
+ed25519-dalek = "2.1.0"
 futures-util = { version = "0.3.28", features = ["io"], optional = true }
 glob = "0.3.0"
 nom = "7.1.3"