v0.3.0 fixes

[Xuechen Li]

Non-structural fixes.

• Convert to make_private style to avoid bad syntax highlighting during static analysis
• Improve the cleanliness of examples
• Refactor test file and use functorch to simplify ground truth gradients' logic
• Don't compute per-sample gradients for weights which don't require gradients
• Use the new smart resizer for tokenizer and model
• Refactor decoding to use new left padding based construction