Format request: Align variables that are next to each other

Given the following example Justfile:

```just
version := "0.2.7"
foo1 := / "tmp"
foo2_3 := "a/"
foo2_bar := "a/"

tmpdir := `mktemp`
project_tardir := tmpdir / "awesomesauce-" + version
prj_tarball := tardir + ".tar.gz"
```

## Current Behavior

When you run `just --unstable --format --check` you get this diff, where every variable only has a single space around the assignment operator and the blank line between them removed:

```diff
version := "0.2.7"
-foo1 := / "tmp"
+foo1 := / "tmp"
foo2_3 := "a/"
-foo2_bar := "a/"
-
-tmpdir := `mktemp`
+foo2_bar := "a/"
+tmpdir := `mktemp`
project_tardir := tmpdir / "awesomesauce-" + version
prj_tarball := project_tardir + ".tar.gz"
```

## Wanted Behavior

My preference would be to have the formatted output preserve the blank line and add spacing to the left of the operator to visually align them vertically, resulting in the following:

```just
version := "0.2.7"
foo1 := / "tmp"
foo2_3 := "a/"
foo2_bar := "a/"

tmpdir := `mktemp`
project_tardir := tmpdir / "awesomesauce-" + version
prj_tarball := project_tardir + ".tar.gz"
```

Where each blank-separated block of variables has it's own alignment, and there are _n_ spaces to cause the `:=` to be vertically aligned.

*(Just version 1.25.2 on MacOS)*

Start at the formatter entry point used by `just --unstable --format --check`, then trace how variable assignments and blank-separated blocks are formatted. Done means each block aligns its `:=` operators independently, blank lines are preserved, and the example produces the requested output without a formatting diff.

Written by the indexing model from the issue text.