Add RecordSeries::get_record and support for (my_ticks 0)

This commit introduces the `get_record` method to `RecordSeries`,
allowing for the dynamic reconstruction of a full record from its
constituent fields at a given index. This enables idiomatic access to
series data using indexing like `(my_ticks 0)`.

The `push-series` function has also been updated to correctly handle the
structure of records when pushing data into a `RecordSeries`.

src/ast/vm.rs

@@ -547,6 +547,24 @@ impl VM {
                                 } else {
                                     break Err("Series index must be an integer".to_string());
                                 }
+                            } else if let Some(rs) = obj.as_any().downcast_ref::<crate::ast::rtl::series::RecordSeries>() {
+                                // Support for `(my_ticks 0)` - reconstructs the full Record from SoA!
+                                if arg_vals.len() != 1 {
+                                    break Err("RecordSeries indexer expects exactly 1 argument (the lookback index)".to_string());
+                                }
+                                if let Value::Int(idx) = arg_vals[0] {
+                                    if idx < 0 {
+                                        break Err("RecordSeries lookback index cannot be negative".to_string());
+                                    }
+                                    if let Some(rec) = rs.get_record(idx as usize) {
+                                        break Ok(rec);
+                                    } else {
+                                        // Out of bounds / not enough data yet
+                                        break Ok(Value::Void);
+                                    }
+                                } else {
+                                    break Err("RecordSeries index must be an integer".to_string());
+                                }
                             } else {
                                 break Err(format!("Object is not callable: {}", obj.type_name()));
                             }