[emulator] Mask memory-read-hook value to the buffer width in Python

The Python memory-read hook did result.to_bytes(buf_len, ...), which raises
OverflowError if the hook returns a value that does not fit in buf_len bytes;
the bare except then swallowed it and silently returned False, dropping a valid
hook result. Mask the value to the buffer width first (matching the C++ bridge's
truncating behavior) so it is stored instead.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: xusheng6

plugins/emulator/api/python/ilemulator.py

@@ -393,7 +393,11 @@ def _cb(ctxt, emu, addr, size, out_buf, buf_len):
             try:
                 result = self._memory_read_hook(self, addr, size)
                 if result is not None:
-                    raw = result.to_bytes(buf_len, 'little', signed=(result < 0))
+                    # Mask to the buffer width so a value that does not fit (or is negative)
+                    # is truncated to its low bytes instead of raising OverflowError and
+                    # silently dropping the hook result.
+                    mask = (1 << (buf_len * 8)) - 1
+                    raw = (result & mask).to_bytes(buf_len, 'little')
                     for i in range(buf_len):
                         out_buf[i] = raw[i]
                     return True