feat(asm): Phase E — multi-output asm returns tuples

Replaces the N>1 "Phase E" bail with a shared asmResultType helper (lowering +
inferType) that derives the result type from the out_value operands: 0→void,
1→T, N→a named tuple (fields named via the §II.5 effective-name rule).

Key realization: toLLVMType(tuple) already produces a literal struct {T1,…,Tn} —
exactly what LLVM's multi-output inline asm returns — so emit needs NO change.
Building the op with a tuple result type makes the asm call return the struct,
which IS sx's tuple value (destructured by the normal tuple_get path).

inferType's .asm_expr arm now also delegates to asmResultType (single owner), so
`return asm`, `x := asm`, and `q, r := asm` all agree on the type.

Verified end-to-end on aarch64: split(0x1234)→(lo=52,hi=18), a udiv/msub
divmod→(3,2). IR: `call { i64, i64 } asm "divq ${4}",
"={rax},={rdx},{rax},{rdx},r,~{cc}"(…)` → extractvalue → tuple.

1640 → the x86_64 multi-output IR lock (ir-only); 1647 → a multi-output example
that runs on aarch64.

zig build test green (655 corpus, 446 unit).

examples/expected/1640-platform-asm-parse.stderr

@@ -1,17 +1 @@
-error: multi-output (tuple-returning) inline assembly is not yet implemented (ASM stream Phase E)
-  --> examples/1640-platform-asm-parse.sx:9:12
-   |
- 9 |     return asm {
-   |            ^^^^^
-10 |         "divq %[d]",
-   | ^^^^^^^^^^^^^^^^^^^^
-11 |         [quot] "={rax}" -> u64,
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-12 |         [rem]  "={rdx}" -> u64,
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-13 |         "{rax}" = n,  "{rdx}" = 0,  [d] "r" = d,
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-14 |         clobbers(.cc),
-   | ^^^^^^^^^^^^^^^^^^^^^^
-15 |     };
-   | ^^^^^
+