Function is_singular_of 

pub fn is_singular_of(singular: &str, plural: &str) -> bool

Check if a singular word could be the singular form of a plural word.

This is useful for matching node names to field names in deserialization:

• is_singular_of("dependency", "dependencies") → true
• is_singular_of("child", "children") → true
• is_singular_of("item", "items") → true

This function is allocation-free when possible.