memtrack: VLA from map2check_map_non_static_alloca is a leak and takes size in bytes (SD-12) #38

map2check_map_non_static_alloca (used for variable-length arrays) differs from the legacy call in two ways. Documented as SD-12 in docs/semantic-deltas.md (PR #35).

1. It marks the record dynamic, so with map2check_set_memcleanup() on, a VLA that goes out of scope reports MEMSAFETY_MEMCLEANUP.
2. It stores size in bytes; the legacy contract passes an element count and multiplies by size_of_primitive. A caller following the legacy contract registers a block that is too small, and loads past it report MEMSAFETY_DEREF.

Reproduce (links against libmap2check.a, no features):

map2check_init();
int n = 4; int vla[n];
map2check_map_non_static_alloca("vla", vla, sizeof(vla), sizeof(int), 3, 0);
map2check_set_memcleanup();
map2check_check_mem_endprog();   /* MemsafetyMemcleanup */

map2check_reset();
map2check_map_non_static_alloca("vla", vla, n, sizeof(int), 3, 0);  /* legacy: element count */
map2check_check_load(&vla[2], 4, 0, sizeof(int), "main");          /* MemsafetyDeref; legacy: valid */

Legacy: map2check_non_static_alloca calls map2check_alloca(name, ptr, size * size_of_primitive, ...), a static slot (lib_old/AnalysisModeMemtrack.c:366-377 on origin/refactory_memory_log).

Likely cause: entry.set_malloc() and size as usize in map2check_map_non_static_alloca (rust/src/ffi.rs). The Rust semantics were reconstructed without the original source (see docs/api-deltas.md).

Pinned today by: rust/src/ffi_tests.rs::map_non_static_alloca_records_dynamic_slot, ::non_static_alloca_is_reported_as_leak_at_end_of_program, ::non_static_alloca_size_is_bytes_not_element_count.

Acceptance criteria:

• Decide both points, considering the signature the Map2Check pass uses (map2check_non_static_alloca(ptr, ptr, i64, i64, i64, i64), see Add a compatibility layer for current Map2Check passes #21).
• Update the tests, SD-12 and the map2check_map_non_static_alloca section of docs/api-deltas.md in the same change.