Function pascal_to_snake 

pub fn pascal_to_snake(name: &str) -> String

Convert a PascalCase or mixed-case name to snake_case with correct acronym handling.

Use this instead of heck::ToSnakeCase when the input is a PascalCase Rust type or enum variant name — heck inserts an underscore before every uppercase letter, which incorrectly splits acronym-style names like Rdfa into rd_fa.

Rules:

• A run of consecutive uppercase letters is treated as a single acronym word.
• If the run is followed by a lowercase letter, the last uppercase char begins the next word (e.g. XMLHttp → xml_http).
• A single uppercase letter followed by lowercase is a normal word start.

Examples:

• MyType → my_type
• Rdfa → rdfa
• HTMLParser → html_parser
• XMLHttpRequest → xml_http_request
• IOError → io_error
• URLPath → url_path
• JSONLD → jsonld