ir: clear wide_hi between functions to fix 16-bit op aliasing

The IrLowerer's wide_hi map records "this u8 temp's high byte
lives at this other temp" pairs whenever a 16-bit value is
produced. Both lower_function and lower_handler reset next_temp
to 0 at the start of each function, but neither cleared wide_hi
— so stale (low_id -> high_id) entries from earlier functions
leaked into subsequent ones.

When a fresh function reused those temp IDs for unrelated u8
expressions, is_wide() returned spurious true and widen() handed
back stale (lo, hi) pairs whose hi happened to coincide with the
*next* temp ID fresh_temp() was about to allocate. The result
was 16-bit IR ops (CmpEq16 in particular) where the destination
temp aliased one of the source operand high bytes — for War this
made `match phase` arms past P_WIN_B impossible to enter and the
game would freeze with both face-up cards on the table forever.

Fix: clear wide_hi alongside the next_temp reset in both
lower_function and lower_handler. Adds a regression test
(ir::tests::wide_hi_does_not_leak_between_functions) that
constructs a function whose body has no u16 ops but follows a
function that does, and asserts no CmpEq16 op aliases its dest
with an operand high byte.

Also:
- Convert the war Playing state's phase machine from an
  if-chain to a `match`, which is what tripped this bug to the
  surface (it was lurking in earlier ROMs too but their layouts
  never produced the dest/source collision shape).
- Refactor begin_draw_a/b to set fly_card / fly_face_up via
  globals before calling arm_fly, since arm_fly only takes 4
  params (the v0.1 ABI limit, now diagnosed by E0506).
- Hoist the P_RESOLVE comparison result to the global pf_result
  to dodge the param-clobbering issue documented in
  examples/war/COMPILER_BUGS.md §2.
- Document the bug as item #6 in COMPILER_BUGS.md with a
  minimal repro and reproducer-test pointer.
- Refresh the war golden + audio hash to match the new ROM.

https://claude.ai/code/session_0143dTgh3UeRrtfHgQwzcv5z

tests/emulator/goldens/war.audio.hash

@@ -1 +1 @@
-37075c32 132084
+4651593c 132084