Add process-scoped scanning algorithms: multi-pattern, code-xref, pointer-map, dissection, snapshot diff

All are OS-agnostic handlers keyed by vmie_mem* + cr3, built on the windowed
sweep / region walk / matcher; none names a Windows concept and each compiles
against include/ alone.

Scanning: a compiled multi-pattern automaton (Aho-Corasick over each pattern's
longest literal anchor, then a masked verify) finds N signatures in one sweep
pass (sigscan.h sigset; scan.h gva_sig_scan_multi). gva_code_xref decodes
rel32 call/jmp and RIP-relative lea/mov to find every instruction targeting a
given VA.

Pointer graph (pmap.h): one sweep indexes every qword whose value lands in a
mapped region into reverse + forward edges. pmap_referrers is the keystone -
it answers who-points-here, class-instance enumeration (referrers of a vtable
VA), and string xref (referrers of a string VA) from the same index;
pmap_paths is the indexed counterpart to scan_pointer's one-shot DFS;
struct_dissect classifies the qwords of an instance (pointer/vtable/float/
int/string) into a field map.

Temporal (snapdiff.h): snap_take captures a window's bytes, snap_diff reports
the changed runs against a later read.

CMakeLists.txt

@@ -18,7 +18,11 @@ add_library(vmie STATIC
         src/engine/win32/profile.c
         src/engine/win32/text.c
         src/handlers/scan.c
-        src/handlers/sigscan.c)
+        src/handlers/sigscan.c
+        src/handlers/sigset.c
+        src/handlers/codescan.c
+        src/handlers/pmap.c
+        src/handlers/snapdiff.c)
 target_include_directories(vmie
         PUBLIC  ${CMAKE_CURRENT_SOURCE_DIR}/include              # public API: include/*.h
         PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src/core/include     # private: core.h