Complete Phase 8.9: Transparency system removed, explicit birth() working, weak references nullified on fini

Co-authored-by: moe-charm <217100418+moe-charm@users.noreply.github.com>

src/parser/expressions.rs

@@ -506,6 +506,10 @@ impl NyashParser {
                     self.advance();
                     "pack".to_string()
                 }
+                TokenType::BIRTH => {
+                    self.advance();
+                    "birth".to_string()
+                }
                 _ => {
                     let line = self.current_token().line;
                     return Err(ParseError::UnexpectedToken {