Snipets tooling update

- update README
- generate-md.py: ignore trailing newlines when complaining about diffs
- all langs: add more dependencies to templates
- all langs: support @hide-start and @hide-end for multi-line hiding
- go: also allow one-line imports
- java: allow declarations other than `main` method
- python, typescript: implement `unshorten` for implicit imports and
  client initialization
- python: add mypy config as `datasets` lacks type py.typed
- python: hide `# mypy:` annotations
- typescript: add tsconfig that allows top-level `await`s
- typescript: depend on @types/node to fix `import ... from "crypto"`

automation/snippets/migrate-snippet.py

@@ -34,8 +34,9 @@ def main() -> None:
             log(f"Skipping unknown language file: {md_file}")
             continue
 
-        lines = md_file.read_text().rstrip().splitlines()
+        lines = md_file.read_text().strip().splitlines()
         if not lines[0].startswith("```") or lines[-1] != "```":
+            log(f"Can't parse snippet file: {md_file}, skipping")
             continue
         content = "\n".join(lines[1:-1]) + "\n"
         content = lang.unshorten(content)