Signed integer overflow when SipHasher processes inputs >= 2 GB.

Live demo:

```
$ src/test/fuzz/simplest_possible_siphash_fuzzer -rss_limit_mb=8000 crash-061a172add013c03beedf57eb2a121a8289696af
crypto/siphash.cpp:56:10: runtime error: signed integer overflow: 2147483647 + 1 cannot be represented in type 'int'
$ cat src/test/fuzz/simplest_possible_siphash_fuzzer.cpp
#include <cstdint>
#include <vector>

#include <crypto/siphash.h>

void test_one_input(const std::vector<uint8_t>& buffer)
{
    CSipHasher(0, 0).Write(buffer.data(), buffer.size()).Finalize();
}
```

Credits to @elichai who submitted a differential SipHasher fuzzer in #19920 and @guidovranken who first spotted the issue. Thanks!

**Remember: don't trust -- fuzz! :)**
d = val.GetUint64(2);
    v3 ^= d;
    SIPROUND;
    SIPROUND;
    v0 ^= d;
    d = val.GetUint64(3);
    v3 ^= d;
    SIPROUND;
    SIPROUND;
    v0 ^= d;
    v3 ^= ((uint64_t)4) << 59;
    SIPROUND;
    SIPROUND;
    v0 ^= ((uint64_t)4) << 59;
    v2 ^= 0xFF;
    SIPROUND;
    SIPROUND;
    SIPROUND;
    SIPROUND;
    return v0 ^ v1 ^ v2 ^ v3;
}
uint64_t SipHashUint256Extra(uint64_t k0, uint64_t k1, const uint256& val, uint32_t extra)
{
    
    uint64_t d = val.GetUint64(0);
    uint64_t v0 = 0x736f6d6570736575ULL ^ k0;
    uint64_t v1 = 0x646f72616e646f6dULL ^ k1;
    uint64_t v2 = 0x6c7967656e657261ULL ^ k0;
    uint64_t v3 = 0x7465646279746573ULL ^ k1 ^ d;
    SIPROUND;