fix(gen): list iteration loads the real element type

`for v in list[T]` allocated the loop variable as i8* and loaded each
element through i8*, so integer elements were treated as pointers. A
later reuse of the same name, e.g.

    for i in nums:  ...          # i becomes i8*
    for i in range(6): ...       # stores/compares 6 in the i8* slot

then materialized a pointer-typed constant 6 and failed the renderer
with `[MLIR-FAIL] unsupported constant operand form (type '!llvm.ptr',
value '6')`.

Resolve the element type from the list specialization
(`_list_elem_type_from_name`: list[int] -> i32, list[str] -> i8*) and use
it for both the loop-variable alloca and the element load; fail fast when
the specialization name cannot be resolved instead of silently loading a
pointer.

Probe: `for v in list[int]` prints 10/20/30 and sums 60; the reporting
project compiles and runs without the MLIR failure; self-host 110/110;
ListTest, GenericTest3, PtrOpProbe and HashLibTest pass.

App/lib/core/Gen/Stmt/StmtGenCifMixin.vp

@@ -2023,11 +2023,22 @@ novirtual class StmtGenCifMixin:
         if cnt_ptr is None: self.Gen.TypeGenErr.fatal_error(for_node, "list iteration: failed to locate __count__")
         count_val: mlirlite.Value* = mlirlite.build_load(builder, i64_ty, cnt_ptr)
 
-        # loop-var alloca (element type i8*, matching inline list.get)
+        # loop-var alloca (the real element type: list[int] -> i32, list[str] -> i8*).
+        # A fixed i8* slot made `for i in list[int]` store a pointer-typed element and
+        # poisoned later reuse of the same name (e.g. a following `for i in range(6)`
+        # stored/compared integer 6 against an i8* slot).
+        lst_st: mlirlite.LLVMType* = self.Gen.StructGen.get_struct_type_from_value(list_val)
+        lst_nm: str = None
+        if lst_st is not None: lst_nm = mlirlite.get_struct_name(lst_st)
+        elem_ty: mlirlite.LLVMType* = None
+        if lst_nm is not None: elem_ty = self.Gen.ExprGenName._list_elem_type_from_name(pool, lst_nm)
+        if elem_ty is None:
+            self.Gen.TypeGenErr.fatal_error(for_node, "list iteration: cannot determine the list element type (unresolved list[...] specialization)", "TypeError")
+            return 0
         var_alloca: mlirlite.Value* = self.Gen.VarGen.lookup_var(trans.SymTab, var_name)
         new_vars: int = 0
         if var_alloca is None:
-            var_alloca = self.Gen.VarGen._alloca_at_entry(builder, i8_ptr_ty)
+            var_alloca = self.Gen.VarGen._alloca_at_entry(builder, elem_ty)
             if self.Gen.VarGen.define_var(trans.SymTab, var_name, var_alloca) == 0: new_vars = 1
 
         # implicit index variable (i64, aligned with __count__)
@@ -2071,7 +2082,7 @@ novirtual class StmtGenCifMixin:
         esize: mlirlite.Value* = mlirlite.build_load(builder, i64_ty, epp)
         offset: mlirlite.Value* = mlirlite.build_mul(builder, cur_idx, esize)
         elem_addr: mlirlite.Value* = mlirlite.build_gep(builder, i8_ty, data_ptr, offset)
-        cur_elem: mlirlite.Value* = mlirlite.build_load(builder, i8_ptr_ty, elem_addr)
+        cur_elem: mlirlite.Value* = mlirlite.build_load(builder, elem_ty, elem_addr)
         mlirlite.build_store(builder, cur_elem, var_alloca)
 
         # save the old loop context and set break/continue targets