fix: support class instances and typed arrays returned from function calls

[cs01]

Functions returning class instances or typed arrays (e.g. KV[]) previously caused segfaults or LLVM errors because the compiler lost type information at the call site.

What was broken:

• const x = makeObj() where makeObj() returns a class → segfault (field access read wrong memory)
• const tree = buildTree() with self-referential class fields → segfault on deep member access
• const pairs = buildPairs(50) returning KV[] → LLVM opt error (ptr vs double type mismatch)

Root cause: The variable allocator and global variable declarations didn't handle call expressions that return class instances or typed arrays — only new and method_call were supported.

Fix:

• allocateClassInstance now handles call by looking up the function's return type to determine the class name
• Global variable declarations now detect class and array return types from function calls
• Added 3 test fixtures covering all crash patterns