Add function inventory (.pdata), signature generation, and export/PDB symbols

Three reversing capabilities on the win32 surface plus a pure sig-gen handler:

- vmie_win32_functions enumerates a module's functions from the exception
  directory (.pdata RUNTIME_FUNCTION), folding unwind chain continuations into
  their primary - authoritative non-leaf boundaries, not prologue heuristics.
- vmie_win32_exports resolves the export table to {name, rva, ordinal,
  forwarded}: named functions with no PDB or network. vmie_win32_pdb_ref pulls
  the CodeView/RSDS {guid, age, pdb} from the debug directory - the symbol-server
  key for any module (full PDB parsing stays out of scope).
- sig_generate (siggen.h) builds a unique masked signature for a code span,
  wildcarding the rel/RIP-relative displacement bytes the x86 decoder locates and
  growing until it matches the scope exactly once - the dual of sigscan.

The decoder now also reports disp_off/disp_len so a caller can mask the floating
bytes. The MZ/PE walk gains one shared data-directory accessor and one shared
CodeView/RSDS parser; the kernel bootstrap is moved onto both, removing its
private copies - one PE parser in the tree.

CMakeLists.txt

@@ -21,6 +21,7 @@ add_library(vmie STATIC
         src/handlers/sigscan.c
         src/handlers/sigset.c
         src/handlers/codescan.c
+        src/handlers/siggen.c
         src/handlers/x86dec.c
         src/handlers/pmap.c
         src/handlers/snapdiff.c)