fix issue 0143: pack-as-[]Type built as []Any — build it as []type_value

buildPackSliceValue (lower/pack.zig) materialized a bare `$<pack>` []Type slice
as []Any (16-byte elements) — a stale mapping from before the dedicated Type
builtin (.type_value, 8 bytes) replaced Type -> .any. It stored 8-byte const_type
words into 16-byte slots, so a []Type reader (8-byte stride) read [t0, pad, t1, ...]
instead of [t0, t1, ...]. The legacy interp's tagged-Value model hid it; the
byte-accurate comptime VM exposed it (a `..$args` pack forwarded as a []Type
argument across a call read its elements shifted/garbled).

Fix: build the pack-slice array + slice as .type_value (8 bytes). Removed the
stopgap type_name .unresolved guard (379ed05) now that the root cause is fixed.

Regression test examples/0525-packs-pack-as-type-slice-arg.sx (outer(42,"hi",true)
-> inner($args: []Type) -> "i64 string bool"). 700/0 both gates; issue 0143 RESOLVED.

examples/0525-packs-pack-as-type-slice-arg.sx

@@ -0,0 +1,26 @@
+// Regression (issue 0143): a variadic `..$args` pack forwarded as a `[]Type`
+// ARGUMENT across a call must read the right element types. The pack-slice
+// materialization (`buildPackSliceValue`) built a `[]Any` (16-byte) array while
+// `Type` is now `.type_value` (8 bytes) — so a `[]Type` reader (8-byte stride)
+// read `[t0, pad, t1, …]` instead of `[t0, t1, …]`. The legacy interp's
+// tagged-Value model hid it; the byte-accurate comptime VM exposed it.
+#import "modules/std.sx";
+
+inner :: (args: []Type) -> string {
+    s := "";
+    i : i64 = 0;
+    while i < args.len {
+        s = concat(s, type_name(args[i]));
+        s = concat(s, " ");
+        i = i + 1;
+    }
+    return s;
+}
+
+outer :: (..$args) -> string { return inner($args); }
+
+R :: #run outer(42, "hi", true);
+
+main :: () {
+    print("[{}]\n", R);
+}

examples/expected/0525-packs-pack-as-type-slice-arg.exit

@@ -0,0 +1 @@
+0

examples/expected/0525-packs-pack-as-type-slice-arg.stderr

@@ -0,0 +1 @@
+

examples/expected/0525-packs-pack-as-type-slice-arg.stdout

@@ -0,0 +1 @@
+[i64 string bool ]