Zed nightly: Add builtin Pyrefly language server support (#44262)

I'm continuing the work of @lolpack's PR
#40953. This makes it such
that user no longer needs to install the external pyrefly extension to
use pyrefly. It also auto-downloads Pyrefly binary when there's no
existing installation, which the pyrefly extension currently can't do.

We don't publish Pyrefly release artifacts to github (yet), so the
easiest way to obtain a Pyrefly installation is with PyPI. Given that
the PyLSP adapter is already doing a PyPI-based installation, I've
essentially copy&pasted most of the logic from there into pyrefly
adapter so Pyrefly could work in exactly the same way for now.

There are a lot of code duplications here! My thought was to get the
functionality in first, and I can send followup PRs to extract
duplicated code into common helper functions.

I tested the change in 2 scenarios:

• No pyrefly binary is found in $PATH
• There's an existing pyrefly binary in $PATH -- I obtained it with
  uv tool install pyrefly.
  In both scenarios I ran the test by removing the Pyrefly exteranl
  plugin, start Zed, open a .py file with type errors in it, and verify
  that cmd-click (gotodef) works.

Console output for scenario 1:

> cargo run
    Blocking waiting for file lock on package cache
    Blocking waiting for file lock on package cache
    Blocking waiting for file lock on package cache
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 31.62s
     Running `target/debug/zed`
2025-12-04T20:58:07-08:00 INFO  [zed] ========== starting zed version 0.217.0+dev.65f328bd614282c1c370672106a9a279f8f22a3a, sha 65f328b ==========
2025-12-04T20:58:08-08:00 WARN  [zed::reliability] Minidump endpoint not set
2025-12-04T20:58:08-08:00 INFO  [extension_host] extensions updated. loading 2, reloading 0, unloading 0
2025-12-04T20:58:08-08:00 WARN  [audio::audio_settings] Denoise does not work on debug builds, not enabling
2025-12-04T20:58:08-08:00 INFO  [workspace] Rendered first frame
2025-12-04T20:58:09-08:00 WARN  [audio::audio_settings] Denoise does not work on debug builds, not enabling
2025-12-04T20:58:16-08:00 INFO  [lsp] starting language server process. binary path: "/Users/grievejia/Library/Application Support/Zed/languages/ruff/ruff-0.14.8/ruff-aarch64-apple-darwin/ruff", working directory: "/Users/grievejia/scratch/pyre_test", args: ["server"]
2025-12-04T20:58:20-08:00 INFO  [lsp] starting language server process. binary path: "/Users/grievejia/Library/Application Support/Zed/languages/pyrefly/pyrefly-venv/bin/pyrefly", working directory: "/Users/grievejia/scratch/pyre_test", args: ["lsp"]
...

We could see that the venv installation is successful and the
auto-installed Pyrefly binary is used.

Console output for scenario 2:

> cargo run
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 29.62s
     Running `target/debug/zed`
2025-12-04T21:01:26-08:00 INFO  [zed] ========== starting zed version 0.217.0+dev.65f328bd614282c1c370672106a9a279f8f22a3a, sha 65f328b ==========
2025-12-04T21:01:27-08:00 WARN  [zed::reliability] Minidump endpoint not set
2025-12-04T21:01:27-08:00 INFO  [extension_host] extensions updated. loading 2, reloading 0, unloading 0
2025-12-04T21:01:27-08:00 WARN  [audio::audio_settings] Denoise does not work on debug builds, not enabling
2025-12-04T21:01:27-08:00 INFO  [workspace] Rendered first frame
2025-12-04T21:01:28-08:00 WARN  [audio::audio_settings] Denoise does not work on debug builds, not enabling
2025-12-04T21:01:34-08:00 INFO  [language] found user-installed language server for pyrefly. path: "/Users/grievejia/.local/bin/pyrefly", arguments: ["lsp"]
2025-12-04T21:01:34-08:00 INFO  [lsp] starting language server process. binary path: "/Users/grievejia/.local/bin/pyrefly", working directory: "/Users/grievejia/scratch/pyre_test", args: ["lsp"]

We could see that the correct installed Pyrefly binary was picked up.

Release Notes:

• Added Pyrefly as builtin language server option

---

Co-authored-by: Piotr Osiewicz 24362066+osiewicz@users.noreply.github.com