fix(pypi): slim sdist inherited from crate allowlist; keep type stub (0.2.4) (#153)

The 0.2.3 sdist was 10.09 MiB (packaged tests/fixtures). maturin derives
the sdist file list from Cargo's include allowlist, so it's now 1.35 MiB
— but the allowlist dropped pdf_inspector.pyi, which would strip type
hints from wheels built from the sdist. Add it back and bump to 0.2.4.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Cargo.toml

@@ -16,6 +16,9 @@ include = [
     "external/bcmaps/**",
     "docs/rust-api.md",
     "LICENSE",
+    # maturin derives the sdist file list from this allowlist; the stub must
+    # ship so wheels built from the sdist keep their type hints.
+    "pdf_inspector.pyi",
 ]
 
 [lib]