GHSA-2c6h-4899-wjxr: scaly: Multiple soundness issues in Rust safe APIs

Affected versions contain multiple safe APIs that can trigger undefined behavior:

• Array<T>::index can perform an out-of-bounds read.
• String::get_length can perform an out-of-bounds read.
• String::append_character can perform an invalid write.
• String::to_c_string can perform an out-of-bounds write.

These issues were reproduced against scaly 0.0.37 under Miri. The crate is unmaintained.