feat: support module-qualified constructor patterns in match expressions (issue 3)

Added module: Option<Ident> to Pattern::Constructor, updated parser to
handle module.Constructor(args) syntax in patterns, exported ADT
constructors from modules, and copied type definitions during module
import so types like Shape are usable in importing files.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/formatter.rs

@@ -772,12 +772,22 @@ impl Formatter {
             Pattern::Wildcard(_) => "_".to_string(),
             Pattern::Var(ident) => ident.name.clone(),
             Pattern::Literal(lit) => self.format_literal(lit),
-            Pattern::Constructor { name, fields, .. } => {
+            Pattern::Constructor {
+                module,
+                name,
+                fields,
+                ..
+            } => {
+                let prefix = match module {
+                    Some(m) => format!("{}.", m.name),
+                    None => String::new(),
+                };
                 if fields.is_empty() {
-                    name.name.clone()
+                    format!("{}{}", prefix, name.name)
                 } else {
                     format!(
-                        "{}({})",
+                        "{}{}({})",
+                        prefix,
                         name.name,
                         fields
                             .iter()