uuid: avoid using deprecated math/rand.Read

[rafiss]

Now we generate uint64s instead and populate them into the UUID array.

goos: darwin
goarch: arm64
              │ /var/folders/p3/c61_z_vd3r7dr1_hnztm3ryr0000gq/T/tmp.BIfUofSiKJ/bench.0cde11b885a │ /var/folders/p3/c61_z_vd3r7dr1_hnztm3ryr0000gq/T/tmp.BIfUofSiKJ/bench.fbea7746013 │
              │                                      sec/op                                       │                          sec/op                            vs base                │
FastMakeV4-10                                                                         22.20n ± 0%                                                 28.34n ± 1%  +27.69% (p=0.000 n=10)

              │ /var/folders/p3/c61_z_vd3r7dr1_hnztm3ryr0000gq/T/tmp.BIfUofSiKJ/bench.0cde11b885a │ /var/folders/p3/c61_z_vd3r7dr1_hnztm3ryr0000gq/T/tmp.BIfUofSiKJ/bench.fbea7746013 │
              │                                       B/op                                        │                             B/op                               vs base            │
FastMakeV4-10                                                                          0.000 ± 0%                                                      0.000 ± 0%  ~ (p=1.000 n=10) ¹
¹ all samples are equal

              │ /var/folders/p3/c61_z_vd3r7dr1_hnztm3ryr0000gq/T/tmp.BIfUofSiKJ/bench.0cde11b885a │ /var/folders/p3/c61_z_vd3r7dr1_hnztm3ryr0000gq/T/tmp.BIfUofSiKJ/bench.fbea7746013 │
              │                                     allocs/op                                     │                           allocs/op                            vs base            │
FastMakeV4-10                                                                          0.000 ± 0%                                                      0.000 ± 0%  ~ (p=1.000 n=10) ¹
¹ all samples are equal

fixes #110597
Release note: None

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[rafiss]

@bdarnell I gave this a shot, and it made the function ~28% slower. Is there a faster way to populate the backing UUID array?

[bdarnell]

I don't think there's a faster way to populate the array; I checked on godbolt.org and the encoding/binary functions appear to get inlined away. It must be a difference between the two calls to Uint64 vs one call to Read. Maybe because there are two lock acquisitions now? (Maybe. I also see references to a non-locking fast path in the math/rand source code but I haven't dug down to exactly what's happening)

Anyway, that's a pretty steep performance penalty just to avoid a deprecated function so I think I'd just leave it alone for now. Maybe a non-deprecated Read method (with a different name) will come back in the revised math/rand API.

[rafiss]

I also see references to a non-locking fast path in the math/rand source code but I haven't dug down to exactly what's happening

Were you referring to this change: golang/go@0b9974d? If so, that's only available in go1.21.

---

Anyway, for now I will close this out and leave the linked issue open.

[bdarnell]

Ah yes, that's what I saw.

[rafiss]

I created #110670 since working in this area made me see other worthwhile cleanups