`spack solve` is supposed to show you times you can compare. setup, ground, solve, etc.
all in a list. You're also supposed to be able to compare easily across runs. With
`pretty_seconds()` (introduced in #33900), it's easy to miss the units, e.g., spot the
bottleneck here:
```console
> spack solve --timers tcl
setup 22.125ms
load 16.083ms
ground 8.298ms
solve 848.055us
total 58.615ms
```
It's easier to see what matters if these are all in the same units, e.g.:
```
> spack solve --timers tcl
setup 0.0147s
load 0.0130s
ground 0.0078s
solve 0.0008s
total 0.0463s
```
And the units won't fluctuate from run to run as you make changes.
-[x] make `spack solve` timings consistent like before
be6bb413df