feat: add brace-style syntax for structs and abstracts in ZynML grammar

- Add brace-style struct definitions: struct Point { x: float, y: float }
- Add brace-style abstract definitions with suffix support
- Add struct_field_list and struct_field rules for comma-separated fields
- Add expression-bodied method syntax for impl blocks (fn x(): expr)
- Update stdlib (prelude, collections, tensor) to use brace-style structs
- Update abstract_types example to use brace-style syntax
- Expand e2e tests with syntax_styles module for new grammar features
- All 123 e2e tests passing

Author: darmie

crates/zynml/examples/abstract_types.zynml

@@ -5,37 +5,31 @@ import prelude
 
 // Abstract Duration type with suffix literals
 // Wraps i64 but provides type-safe time operations
-abstract Duration(i64) with Suffixes("ms, s, m"):
-    value: i64
+// Brace-style field definition (recommended for consistency)
+abstract Duration(i64) with Suffixes("ms, s, m") { value: i64 }
 
 // Inherent methods for Duration
 impl Duration(i64) {
-    // Constructor: create from milliseconds
-    fn from_ms(v: i64) -> Duration:
-        Duration { value: v }
+    // Constructor: create from milliseconds (expression-bodied)
+    fn from_ms(v: i64) -> Duration: Duration { value: v }
 
     // Constructor: create from seconds
-    fn from_s(v: i64) -> Duration:
-        Duration { value: v * 1000 }
+    fn from_s(v: i64) -> Duration: Duration { value: v * 1000 }
 
     // Constructor: create from minutes
-    fn from_m(v: i64) -> Duration:
-        Duration { value: v * 60000 }
+    fn from_m(v: i64) -> Duration: Duration { value: v * 60000 }
 
     // Conversion: to milliseconds
-    fn to_ms(self) -> i64:
-        self.value
+    fn to_ms(self) -> i64: self.value
 
     // Conversion: to seconds (integer division)
-    fn to_s(self) -> i64:
-        self.value / 1000
+    fn to_s(self) -> i64: self.value / 1000
 
     // Conversion: to minutes
-    fn to_m(self) -> i64:
-        self.value / 60000
+    fn to_m(self) -> i64: self.value / 60000
 }
 
-fn main():
+fn main() {
     // Demonstrate Duration with suffix literals and method dispatch
 
     // Test 1: milliseconds literal
@@ -60,3 +54,4 @@ fn main():
     let delay5 = Duration::from_s(10)
     println(delay5.to_ms())  // Expected: 10000
     println(delay5.to_s())   // Expected: 10
+}