Migrate `wg.Add(1); go func() { defer wg.Done(); ... }()` to
`wg.Go(func() { ... })` in tests.
Where the prior pattern passed the loop variable explicitly via a
closure parameter (`go func(id int) { ... }(i)`), drop the parameter and
reference the loop variable directly. Per-iteration loop variables since
Go 1.22 make this safe.
The slices package provides type-safe generic replacements for the
old typed sort convenience functions. The codebase already uses
slices.Sort in 43 call sites; this finishes the migration for the
remaining 29.
- sort.Strings(x) -> slices.Sort(x)
- sort.Float64s(x) -> slices.Sort(x)
- sort.StringsAreSorted(x) -> slices.IsSorted(x)
Zach