Optimise CLJS build

Before starting compilation, at the initialization stage, a shadow-cljs launch can take up to **20** seconds, plus we do this twice for the main build and static-viz. The same goes for the compilation itself, which we also do twice, taking **40-50** seconds on CI. If we learn to reuse the previous build, or do it in parallel, we could save about a **minute** on CLJS builds.

```[tasklist]
### Tasks
- [ ] https://github.com/metabase/metabase/issues/37580
- [ ] https://github.com/metabase/metabase/issues/43459
- [ ] https://github.com/metabase/metabase/issues/46706
- [ ] Research a way to reuse the previous build or run `build-frontend` in parallel
```

Start by reviewing issues 37580, 43459, and 46706, then investigate the `build-frontend` work mentioned in the task list. Compare reusing the previous build with running the main build and static-viz compilation in parallel, and measure CI time to confirm that the completed approach saves about a minute.

Written by the indexing model from the issue text.