Function count_top_level_functions 

pub fn count_top_level_functions(ast: &File) -> usize

Count the number of top-level functions in an AST file.

“Top-level” means:

• FunctionDeclaration at program body level
• FunctionExpression/ArrowFunctionExpression in a VariableDeclarator at program body level
• FunctionDeclaration inside ExportNamedDeclaration
• FunctionDeclaration/FunctionExpression/ArrowFunctionExpression inside ExportDefaultDeclaration
• VariableDeclaration with function expressions inside ExportNamedDeclaration

This matches the TS test binary’s traversal behavior.