Fix: Improve series type handling and coercions

This commit enhances the series type handling in `src/ast/rtl/series.rs`
by introducing helper methods `as_float` and `as_int` in
`src/ast/types.rs` to manage type conversions more robustly.

It also updates the function overload resolution in `src/ast/types.rs`
to prioritize exact parameter matches before falling back to implicit
coercions.

Finally, the example `err.myc` has been updated to reflect a more
accurate implementation of a Simple Moving Average (SMA) calculation.

src/ast/rtl/series.rs

@@ -218,19 +218,16 @@ pub trait SeriesMember: Object + Series {
 
 impl SeriesMember for ScalarSeries<f64> {
     fn push_value(&self, value: Value, limit: Option<usize>) {
-        match value {
-            Value::Float(v) => self.data.borrow_mut().push(v, limit),
-            Value::Int(v) => self.data.borrow_mut().push(v as f64, limit),
-            _ => {}
+        if let Some(v) = value.as_float() {
+            self.data.borrow_mut().push(v, limit);
         }
     }
 }
 
 impl SeriesMember for ScalarSeries<i64> {
     fn push_value(&self, value: Value, limit: Option<usize>) {
-        match value {
-            Value::Int(v) | Value::DateTime(v) => self.data.borrow_mut().push(v, limit),
-            _ => {}
+        if let Some(v) = value.as_int() {
+            self.data.borrow_mut().push(v, limit);
         }
     }
 }