Co-authored-by: Turbobot <turbobot@vercel.com>

### Description

🎉

Authors the 2.6 release post and updates documentation for Bun to be
stable.

### Testing Instructions

👀

<sub>CLOSES TURBO-4527</sub>
<sub>CLOSES TURBO-4920</sub>

### Description

<!--
  ✍️ Write a short summary of your work.
  If necessary, include relevant screenshots.
-->

For all of us randoms who thought "hmmm... robobun?"

### Testing Instructions

<!--
  Give a quick description of steps to test your changes.
-->

n/a

### Description

[macOS runners are soon to be
deprecated](actions/runner-images#13046), so
updating them.

### Testing Instructions

CI

### Description

Updating our Bun lockfile parser to achieve full parity with
`--frozen-lockfile`.

### Testing Instructions

I've added fixtures from #11007 and hand-tested each fixture with real
repositories with this newly updated logic. You'll also note that I've
removed some unit testing in favor of snapshot testing. Ultimately, we
care that the lockfile gets pruned and created correctly, which is what
the snapshots are testing for. Given Bun's relatively fast iteration
speed, the internals of how we compute the pruned lockfile don't help as
much for now. We can solidify with unit tests in the future if we need
to.

### Description

Adds `XDG_RUNTIME_DIR` to the list of default global pass-through
environment variables. This ensures that the standard XDG runtime
directory is available in tasks by default.

### Testing Instructions

Verify that `XDG_RUNTIME_DIR` is passed through to tasks by running a
Turborepo task that prints its environment variables (e.g., `echo
$XDG_RUNTIME_DIR`).

CLOSES TURBO-4894

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Co-authored-by: Cursor Agent <cursoragent@cursor.com>