RNG hadning in SRV lookups for public root peers

[Savissy]

Motivation:

The public root peers provider used the same StdGen seed for all DNS lookups, causing SRV weighted-sampling to reuse the same RNG and produce correlated/identical selections across domains.
The change aims to provide independent RNGs per domain lookup so SRV selection becomes varied and correct.

Description:

Add a mutable RNG StrictTVar (rngVar) initialized from the supplied StdGen and thread it into the request path for publicRootPeersProvider by changing the local requestPublicRootPeers signature to accept the RNG var.
Generate one split RNG per domain with replicateM + stateTVar rngVar split and zip those RNGs with the domain list, then pass each domain-specific RNG into dnsLookupWithTTL so lookups (including srvRecordLookupWithTTL) use independent RNGs.
Import replicateM from Control.Monad and create rngVar via newTVarIO near the resolver resource initialization.

[crocodile-dentist]

I don't see a way this can be viably exploited or what actual risk this will mitigate.

[crocodile-dentist]

We've discussed internally and agreed that adding this change won't hurt. Please fix the build failures first.

[coot]

Indentation

Suggested change

	requestPublicRootPeers resourceVar _numRequested = do
	requestPublicRootPeers resourceVar rngVar _numRequested = do
	requestPublicRootPeers resourceVar rngVar _numRequested = do