Fix Linux allocation hook calloc overflow handling

[fallintoplace]

Motivation

The Linux allocation-counting hook implements calloc by multiplying count and size before allocating, then zeroing the result unconditionally. If the multiplication overflows, the hook can allocate a smaller buffer than requested. If allocation fails, it can pass NULL to memset.

Modification

This checks for count/size overflow before multiplying, reuses the computed total size, and only zeroes memory after allocation succeeds.

Result

The Linux hook now follows calloc-style failure behavior for overflow and avoids zeroing a NULL pointer on allocation failure.

Validation

• swift build --package-path IntegrationTests/allocation-counter-tests-framework/template/HookedFunctionsDoHook
• clang -std=gnu11 -fsyntax-only -U__APPLE__ -IIntegrationTests/allocation-counter-tests-framework/template/HookedFunctionsDoHook/Sources/HookedFunctions/include -IIntegrationTests/allocation-counter-tests-framework/template/AtomicCounter/Sources/AtomicCounter/include IntegrationTests/allocation-counter-tests-framework/template/HookedFunctionsDoHook/Sources/HookedFunctions/src/hooked-functions-unix.c