NilPy: bool/char param spill wrote 4 bytes into a 1-byte slot (SILENT, then SIGSEGV)

Pre-existing: the hand-rolled NilPy prologue spilled every param with a dword/qword store regardless of slot size. A tyBoolean param slot is 1 byte, so the store clobbered up to 3 bytes of the neighbouring slots: bool params read back wrong (True -> False), and with more params the clobber reached self and crashed. class J: def __init__(self, p: bool) was enough.

Fixed with PyEmitStoreRaxWidth (width by TypeSize) in the same unit as feature-nilpy-decorators-dataclass / feature-nilpy-def-params.