fix: cookbook guess_version falls back to '0.1.0' instead of None

When recipe has no [package].version, no parseable tar URL version,
no git rev/branch version, no Cargo.toml version, and no directory-name
version — fall back to '0.1.0' instead of failing with 'cannot guess
version'. This eliminates the class of failures for sysroot-copy and
simple git-source recipes like netdb, libgcc, libstdcxx, etc.

src/recipe.rs

@@ -523,7 +523,7 @@ impl CookRecipe {
         if let Some(ver) = VersionExtractor::extract_cargo_ver(&cargo_path) {
             return Some(ver);
         }
-        None
+        Some("0.1.0".into())
     }
 }