Waleed Khan c7b677b86d build: switch back to gix/max-performance-safe feature by default
Using `gix/max-performance` requires `cmake` as a build-time dependency, which could be a significant barrier for contributors (including existing ones, like me, who already work on jj but didn't have `cmake` installed thus far).

This commit switches back to using `gix/max-performance-safe`, which doesn't have the `cmake` dependency, and adds `gix/max-performance` behind the `gix-max-performance` feature for `jj-lib`.

It also adds `gix-max-performance` to the `packaging` feature group, since I'm assuming that packagers will want maximum performance, and are more likely to have `cmake` at hand.

Tested with

```
$ cargo build --workspace
$ cargo build --workspace --features packaging
```

(and the `--features packaging` build failed until I installed `cmake`)
2024-12-31 17:07:52 -06:00
..