Fix singleton bug

compiler-core/templates/echo.mjs

···
       return "//js(circular reference)";
     }
 
-    if (Array.isArray(v))
-      return `#(${v.map((v) => this.inspect(v)).join(", ")})`;
-    if (v instanceof $List) return this.#list(v);
-    if (v instanceof $CustomType) return this.#customType(v);
-    if (this.#isDict(v)) return this.#dict(v);
-    if (v instanceof Set)
+    let printed;
+    if (Array.isArray(v)) {
+      printed = `#(${v.map((v) => this.inspect(v)).join(", ")})`;
+    } else if (v instanceof $List) {
+      printed = this.#list(v);
+    } else if (v instanceof $CustomType) {
+      printed = this.#customType(v);
+    } else if (this.#isDict(v)) {
+      printed = this.#dict(v);
+    } else if (v instanceof Set) {
       return `//js(Set(${[...v].map((v) => this.inspect(v)).join(", ")}))`;
-    return this.#object(v);
+    } else {
+      printed = this.#object(v);
+    }
+    this.#references.delete(v);
+    return printed;
   }
 
   #object(v) {

test-output/cases/echo_singleton/gleam.toml

···
+name = "echo_circular_reference"
+version = "1.0.0"
+target = "javascript"

test-output/cases/echo_singleton/src/main.gleam

···
+import thing
+
+pub fn main() {
+  echo #(1, singleton(), singleton())
+  Nil
+}
+
+@external(javascript, "./main_ffi.mjs", "singleton")
+fn singleton() -> thing.Thing {
+  thing.Thing
+}

test-output/cases/echo_singleton/src/main_ffi.mjs

···
+import { Thing } from "./thing.mjs";
+
+const it = new Thing();
+
+export function singleton() {
+  return it;
+}

test-output/cases/echo_singleton/src/thing.gleam

···
+pub type Thing {
+  Thing
+}

test-output/src/tests/echo.rs

···
 fn echo_circular_reference() {
     assert_echo!(Target::JavaScript, "echo_circular_reference");
 }
+
+#[test]
+fn echo_singleton() {
+    assert_echo!("echo_singleton");
+}

test-output/src/tests/snapshots/test_output__tests__echo__echo_singleton.snap

···
+---
+source: test-output/src/tests/echo.rs
+assertion_line: 206
+expression: output
+snapshot_kind: text
+---
+--- main.gleam ----------------------
+import thing
+
+pub fn main() {
+  echo #(1, singleton(), singleton())
+  Nil
+}
+
+@external(javascript, "./main_ffi.mjs", "singleton")
+fn singleton() -> thing.Thing {
+  thing.Thing
+}
+
+
+--- gleam run output ----------------
+src/main.gleam:4
+#(1, Thing, Thing)