test(asm): lock read-write + place-output rejection (Phase G prep)

Adds examples/1650-platform-asm-rw-place.sx exercising a `+r -> @x`
read-write place output. Currently rejected loudly at lowering
("not yet implemented"); this locks that behavior as a passing test.
The next commit implements read-write outputs and flips this example
to run end-to-end (increment-in-place → 42).

examples/expected/1650-platform-asm-rw-place.exit

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

examples/expected/1650-platform-asm-rw-place.stderr

@@ -0,0 +1,5 @@
+error: read-write (`+`) asm outputs are not yet implemented; use a write-only `=` output
+  --> examples/1650-platform-asm-rw-place.sx:8:5
+   |
+ 8 |     asm volatile { "add %[v], %[v], #1", [v] "+r" -> @x };
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

examples/expected/1650-platform-asm-rw-place.stdout

@@ -0,0 +1 @@
+