Fix int overflow on x32 processors causing panic using burstObservatory

[tekig]

When using burstObservatory I get a panic on the mipsle processor. During the roll, "duration" is converted to int, causing overflow on x32 processors. The value may be very small, causing private queries, or negative, causing a panic in rand.Intn.

Version: Xray 1.8.18 (Xray, Penetrates Everything.) 9e6d7a3c (go1.22.5 linux/mipsle)

Config burstObservatory:

{
    "burstObservatory": {
        "subjectSelector": ["proxy"],
        "pingConfig": {
            "destination": "https://connectivitycheck.gstatic.com/generate_204",
            "connectivity": "",
            "interval": "30s",
            "sampling": 3,
            "timeout": "3s"
        }
    }
}

Stdout:

panic: invalid argument to Intn

goroutine 35 [running]:
math/rand.(*Rand).Intn(0x21139e0, 0xf46b0400)
        math/rand/rand.go:180 +0xd0
math/rand.Intn(0xf46b0400)
        math/rand/rand.go:453 +0x48
github.com/xtls/xray-core/common/dice.Roll(...)
        github.com/xtls/xray-core/common/dice/dice.go:14
github.com/xtls/xray-core/app/observatory/burst.(*HealthPing).doCheck(0x241f820, {0x22853c0, 0x5, 0x8}, 0x14f46b0400, 0x3)
        github.com/xtls/xray-core/app/observatory/burst/healthping.go:159 +0x3c4
github.com/xtls/xray-core/app/observatory/burst.(*HealthPing).StartScheduler.func2.1()
        github.com/xtls/xray-core/app/observatory/burst/healthping.go:100 +0x194
created by github.com/xtls/xray-core/app/observatory/burst.(*HealthPing).StartScheduler.func2 in goroutine 8
        github.com/xtls/xray-core/app/observatory/burst/healthping.go:94 +0xe0

[yuhan6665]

Looks good. Thank you!

[RPRX]

#3774 (comment)