feat: add WrenValue handle API for persistent object references outside VM

Introduce WrenValue type and wrenGetArgumentValue/wrenReleaseValue functions to allow C code to hold GC-safe references to Wren objects across foreign calls. Implement doubly-linked list management in VM struct, mark value handles during garbage collection, and add assertion in wrenFreeVM to detect unreleased values. Update test infrastructure with new get_value test case and rename existing test binding functions to camelCase convention.

test/api/get_value/get_value.wren

@@ -0,0 +1,14 @@
+class Api {
+  foreign static value=(value)
+  foreign static value
+}
+
+Api.value = ["list", "of", "strings"]
+
+// Do some stuff to trigger a GC (at least when GC stress testing enabled).
+var s = "string"
+for (i in 1...10) {
+  s = s + " more"
+}
+
+IO.print(Api.value) // expect: [list, of, strings]