arm64/mem: Refactor guest memory access and made it endian aware

Refactors the core guest memory access subsystem (guest.h) to be safer
and portable accross host systems with different endianness. The
previous implementation used direct pointer casting, which is not endian
safe.

1. All read and write functions have been converted from unsafe pointer
   casts to memcpy(). This resolves alignment warning -Wcast-align.

2. The access functions no longer rely on asserts for error checking.
   They now perform explicit boundary and alignment checking and returns
   a guest_mem_access_result_t status code.

3. A new header (endian.h) provides cross platform byte swapping macros.
   The memory access functions use these macros to ensure that the guest
   always sees memory in the correct endian format, regardless of the
   host's native byte order. The host endianness is now automatically
   detected via CMake.

3. Asserts are now explicitly enabled in release builds to catch
   critical errors.

Signed-off-by: Ronald Caesar <github43132@proton.me>

src/kvm/mmu.cpp

@@ -340,7 +340,8 @@ int mmu_gva_to_gpa(pound::kvm::kvm_vcpu_t* vcpu, guest_memory_t* memory, uint64_
         }
 
         const uint64_t level_entry_address = table_address + (level_index * page_table_entry_size);
-        const uint64_t descriptor = guest_mem_readq(memory, level_entry_address);
+        uint64_t descriptor = 0;
+        guest_mem_readq(memory, level_entry_address, &descriptor);
         uint64_t offset_mask = (1ULL << offset_bits) - 1;
         uint64_t page_offset = gva & offset_mask;
         uint64_t page_address_mask = ~offset_mask;