upgrade rust in Cargo.toml/flake.nix

Looks like this should've happened as part of !479.

Cargo.toml

@@ -13,7 +13,7 @@ edition = "2021"
 # `nix flake update`. If you don't have Nix installed or otherwise don't know
 # how to do this, ping `@charles:computer.surgery` or `@dusk:gaze.systems` in
 # the matrix room.
-rust-version = "1.64.0"
+rust-version = "1.70.0"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 

flake.nix

@@ -40,7 +40,7 @@
         channel = cargoToml.package.rust-version;
 
         # THE rust-version HASH
-        sha256 = "sha256-8len3i8oTwJSOJZMosGGXHBL5BVuGQnWOT2St5YAUFU=";
+        sha256 = "sha256-gdYqng0y9iHYzYPAdkC/ka3DRny3La/S5G8ASj0Ayyc=";
       };
 
       # The system's RocksDB