rustPlatform.fetchCargo: handle custom Cargo.lock patchfiles with validation

Previously, we would asssert that the lockfiles are consistent during the
unpackPhase, but if the pkg has a patch for the lockfile itself then we must
wait until the patchPhase is complete to check.

This also removes an implicity dependency on the src attribute coming from
`fetchzip` / `fetchFromGitHub`, which happens to name the source directory
"source". Now we glob for it, so different fetchers will work consistently.

pkgs/applications/virtualization/crosvm/default.nix

@@ -53,10 +53,7 @@ in
       ./default-seccomp-policy-dir.diff
     ];
 
-  # Delete this on next update; see #79975 for details
-  legacyCargoFetcher = true;
-
-    cargoSha256 = "1d7y07wkliy5qnlyx5zj6ni39avhs3s48sqgvwxm5g5zrahg2a85";
+    cargoSha256 = "1s9nfgfqk140hg08i0xzylnrgrx84dqss0vnvhxnydwy9q03nk7r";
 
     nativeBuildInputs = [ pkgconfig ];