Add series, SMA, and WMA indicators

Introduce new indicators for Simple Moving Average (SMA) and Weighted
Moving Average (WMA), along with their Hull Moving Average (HMA)
derivative.

Also refactors series implementation to use `RefCell` for interior
mutability and adds `SeriesMember` trait for better dynamic series
access. Updates `soa_series.myc` example to reflect new series creation
and push syntax.

src/ast/compiler/binder.rs

@@ -89,16 +89,16 @@ impl FunctionCompiler {
         match self.kind {
             ScopeKind::Root => {
                 let mut globals_map = globals.borrow_mut();
-                if globals_map.contains_key(name) {
-                    return Err(format!(
-                        "Global variable '{}' is already defined.",
-                        name.name
-                    ));
+                if let Some((idx, existing_id)) = globals_map.get(name) {
+                    if *existing_id != identity {
+                        return Err(format!("Variable '{}' is already defined in global scope.", name.name));
+                    }
+                    return Ok(Address::Global(*idx));
+                }
+                let idx = GlobalIdx(globals_map.len() as u32);
+                globals_map.insert(name.clone(), (idx, identity));
+                Ok(Address::Global(idx))
                 }
-                let idx = globals_map.len() as u32;
-                globals_map.insert(name.clone(), (GlobalIdx(idx), identity));
-                Ok(Address::Global(GlobalIdx(idx)))
-            }
             ScopeKind::Local => {
                 let slot = self.scope.define(name, identity)?;
                 Ok(Address::Local(slot))