refactor: use rand.New(rand.NewSource) instead of deprecated rand.Seed

[chengshiwen]

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Deprecated: As of Go 1.20 there is no reason to call Seed with a random value. Programs that call Seed with a known value to get a specific sequence of results should use New(NewSource(seed)) to obtain a local random generator.

[chengshiwen]

@davidby-influx @gwossum

[chengshiwen]

Please review, thanks so much.
@bnpfeife @jdstrand @devanbenz

[davidby-influx]

As I understand the new rand package, calling rand.New returns a generator based on the source provided in the call. That means that setting a new source does not affect the default source used by the top level functions like rand.Float64. If we are setting seeds explicitly, we need to use the *rand.Rand returned by rand.New to generate the values.