vmie_win32_open_ro_fd maps the RAM backing file PROT_READ (via
gpa_from_ro_fd) and does NOT bootstrap; the caller passes a cr3 to each
read call. The read surfaces work this way - sections / functions /
imports / exports / callgraph / hooks, gva_read_text, and the generic
gva_* and scanner surfaces via vmie_win32_mem() - while any write returns
-1 because the mapping is read-only. The RW twin vmie_win32_open_fd and
host_bootstrap are unchanged.