Copies `nbytes` bytes starting at the raw native `address` into a
fresh owned buffer. This is the only way bytes behind a foreign
pointer — for example a `char *` returned by a C function — become an
LPC value. Pass -1 for `nbytes` to copy a NUL-terminated string up to
an internal cap. Decode text with string_decode() once you have the
bytes.
Every call is gated by the master apply valid_ffi("peek", address,
caller) before any memory is touched: reading an arbitrary native
address is a process-memory disclosure primitive (and an unmapped
address would crash the driver), so the master must approve it even
though no foreign code runs.