fix: make path resolution relative to project root

this was already how it mostly behaved but there seemed to be exceptions
like LSP warnings (in these tests themselves)

src/lib.rs

@@ -27,6 +27,10 @@ pub mod file {
         }
     }
 
+    /// Similar to [`include_bytes!`], but it returns a lot more information about the file, like
+    /// its mime type, or its sha256sum (could be changed), all at compile time.
+    ///
+    /// The path is relative to the package's root.
     #[macro_export]
     macro_rules! include_asset {
         ($path:literal) => {