Maps are being returned not as pointers as they are already pointers (#1956)

This was incorrectly attempting to coerce maps/lists as pointers when
Decode does not return them that way.

Added a test that failed before and now passes.
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----

> [!IMPORTANT]
> Fixes incorrect pointer coercion for maps and lists in
`render_value_coercion()` and adds a test to verify the fix.
> 
>   - **Behavior**:
> - Fixes incorrect pointer coercion for maps and lists in
`render_value_coercion()` in `generate_types.rs`.
> - Adds a test case in `cffi_test.go` to verify correct handling of
maps and lists.
>   - **Models**:
>     - Adds `is_map` field to `GoType` struct in `generate_types.rs`.
> - Updates `ToTypeReferenceInTypeDefinition` implementation to set
`is_map` for `FieldType::Map`.
>   - **Misc**:
> - Updates `Decode` calls in `types.go` and `unions.go` to remove
unnecessary pointer dereferencing for maps.
> 
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<!-- ELLIPSIS_HIDDEN -->

Author: tberman

engine/language_client_codegen/src/go/generate_types.rs

@@ -65,6 +65,11 @@ fn render_value_coercion(container_variable_name: &str, field_type: &GoType) ->
             inner_type.name,
             render_value_coercion("__holder", inner_type),
         );
+    } else if field_type.is_slice || field_type.is_map {
+        return format!(
+            "baml.Decode({container_variable_name}).({})",
+            filters::type_name_without_pointer(&field_type.name).unwrap()
+        );
     } else {
         return format!(
             "*baml.Decode({container_variable_name}).(*{})",
@@ -229,6 +234,7 @@ pub struct GoType {
     name: String,
     is_pointer: bool,
     is_slice: bool,
+    is_map: bool,
     is_primitive: bool,
     is_class: bool,
     is_integer: bool,
@@ -530,6 +536,7 @@ impl ToTypeReferenceInTypeDefinition for FieldType {
             is_pointer: self.is_optional(),
             is_union: matches!(simplified, FieldType::Union(_)),
             is_slice: matches!(simplified, FieldType::List(_)),
+            is_map: matches!(simplified, FieldType::Map(_, _)),
             is_primitive: self.is_primitive(),
             is_class: matches!(simplified, FieldType::Class(_)),
             is_integer: matches!(simplified, FieldType::Primitive(TypeValue::Int)),

integ-tests/go/baml_client/types/types.go

@@ -65,6 +65,14 @@ func TestEncodeDecode(t *testing.T) {
 			Name:       &[]string{"John Doe"}[0],
 			Hair_color: &[]b.Color{b.ColorRED}[0],
 		}},
+		{&b.Recipe{
+			Recipe_type: *b.Union__string_breakfast__string_dinnerNewWithString_breakfast(&[]string{"breakfast"}[0]),
+			Ingredients: map[string]b.Quantity{
+				"a": {
+					Amount: *b.Union__int__floatNewWithInt(&[]int64{1}[0]),
+				},
+			},
+		}},
 		// {b.RecursiveUnion(*b.Union__string__Map__string_RecursiveUnionNewWithMap__string_RecursiveUnion(&map[string]b.RecursiveUnion{
 		// 	"key": b.RecursiveUnion(*b.Union__string__Map__string_RecursiveUnionNewWithString(&[]string{"value"}[0])),
 		// 	"key2": b.RecursiveUnion(*b.Union__string__Map__string_RecursiveUnionNewWithMap__string_RecursiveUnion(&map[string]b.RecursiveUnion{