chore: expose lib target + open-path profiling examples

Examples can't import from a bin-only crate, so add a thin lib.rs that
re-exports the existing modules. Used by the new examples that helped
diagnose the freeze fixed in the previous commit.

- examples/time_open: times parse / purge / cache / first-wires phases
- examples/inspect_insert: lists Insert blocks with sub-entity counts
- examples/find_raster: dumps RasterImage path + dimensions

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

examples/find_raster.rs

@@ -0,0 +1,14 @@
+use acadrust::entities::EntityType;
+use acadrust::io::dwg::DwgReader;
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let path = std::env::args().nth(1).unwrap();
+    let doc = DwgReader::from_file(&path)?.read()?;
+    for e in doc.entities() {
+        if let EntityType::RasterImage(img) = e {
+            println!("file_path: {}", img.file_path);
+            println!("size: {} x {}", img.size.x, img.size.y);
+            if let Ok(meta) = std::fs::metadata(&img.file_path) { println!("disk size: {} bytes", meta.len()); }
+        }
+    }
+    Ok(())
+}