[OWK50GA]

Summary

Fix three correctness issues in the Chapter 6 Script implementation:

• Pop the public key before the signature in OP_CHECKSIG, matching the standard stack layout.
• Use a shared Script boolean conversion for final evaluation and OP_VERIFY. Empty data, all-zero bytes, and negative zero evaluate as false; other values evaluate as true without numeric decoding.
• Validate CompactSize prefixes, declared script lengths, and direct/PUSHDATA1/PUSHDATA2 pushes before reading. Truncated or out-of-bounds input returns InvalidData instead of panicking, and pushes cannot consume bytes beyond the declared script body.

Add regression tests for signature stack order, invalid and empty signatures, boolean encodings, malformed input, pushdata boundaries, and multi-byte length prefixes.

Apply rustfmt and remove a redundant borrow in TxOut::repr to satisfy CI's strict Clippy checks.

Validation

• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo build
• cargo test (full suite, including Chapter 6 regressions)
• git diff --check