refactor: rename wrenGetArgument* to wrenGetSlot* and add IS_LIST macro for slot-based API

Migrate the foreign method argument access API from an argument-oriented naming
scheme to a slot-based one, renaming wrenGetArgumentCount to wrenGetSlotCount,
wrenGetArgumentBool to wrenGetSlotBool, and all other argument accessors
accordingly. Update every call site across the VM, modules (io, timer, meta,
random), and test files (benchmark, foreign_class) to use the new names. The
slot getters now assert the correct type at runtime rather than silently
returning defaults, shifting safety responsibility to the caller for
performance. Also add the IS_LIST type-checking macro to wren_value.h alongside
the existing IS_* macros.

src/optional/wren_opt_meta.c

@@ -18,7 +18,7 @@ void metaCompile(WrenVM* vm)
       : AS_CLOSURE(callingFn)->fn->module;
 
   // Compile it.
-  ObjFn* fn = wrenCompile(vm, module, wrenGetArgumentString(vm, 1), false);
+  ObjFn* fn = wrenCompile(vm, module, wrenGetSlotString(vm, 1), false);
   if (fn == NULL) return;
 
   // Return the result. We can't use the public API for this since we have a

src/optional/wren_opt_random.c

@@ -45,7 +45,7 @@ static void randomAllocate(WrenVM* vm)
 
 static void randomSeed0(WrenVM* vm)
 {
-  Well512* well = (Well512*)wrenGetArgumentForeign(vm, 0);
+  Well512* well = (Well512*)wrenGetSlotForeign(vm, 0);
 
   srand((uint32_t)time(NULL));
   for (int i = 0; i < 16; i++)
@@ -56,9 +56,9 @@ static void randomSeed0(WrenVM* vm)
 
 static void randomSeed1(WrenVM* vm)
 {
-  Well512* well = (Well512*)wrenGetArgumentForeign(vm, 0);
+  Well512* well = (Well512*)wrenGetSlotForeign(vm, 0);
 
-  srand((uint32_t)wrenGetArgumentDouble(vm, 1));
+  srand((uint32_t)wrenGetSlotDouble(vm, 1));
   for (int i = 0; i < 16; i++)
   {
     well->state[i] = rand();
@@ -67,17 +67,17 @@ static void randomSeed1(WrenVM* vm)
 
 static void randomSeed16(WrenVM* vm)
 {
-  Well512* well = (Well512*)wrenGetArgumentForeign(vm, 0);
+  Well512* well = (Well512*)wrenGetSlotForeign(vm, 0);
 
   for (int i = 0; i < 16; i++)
   {
-    well->state[i] = (uint32_t)wrenGetArgumentDouble(vm, i + 1);
+    well->state[i] = (uint32_t)wrenGetSlotDouble(vm, i + 1);
   }
 }
 
 static void randomFloat(WrenVM* vm)
 {
-  Well512* well = (Well512*)wrenGetArgumentForeign(vm, 0);
+  Well512* well = (Well512*)wrenGetSlotForeign(vm, 0);
 
   // A double has 53 bits of precision in its mantissa, and we'd like to take
   // full advantage of that, so we need 53 bits of random source data.
@@ -97,7 +97,7 @@ static void randomFloat(WrenVM* vm)
 
 static void randomInt0(WrenVM* vm)
 {
-  Well512* well = (Well512*)wrenGetArgumentForeign(vm, 0);
+  Well512* well = (Well512*)wrenGetSlotForeign(vm, 0);
 
   wrenReturnDouble(vm, (double)advanceState(well));
 }