… with options to log to a file (#11747)

## Summary

Fixes #10968.
Fixes #11545.

The server's tracing system has been rewritten from the ground up. The
server now has trace level and log level settings which restrict the
tracing events and spans that get logged.

* A `logLevel` setting has been added, which lets a user set the log
level. By default, it is set to `"info"`.
* A `logFile` setting has also been added, which lets the user supply an
optional file to send tracing output (it does not have to exist as a
file yet). By default, if this is unset, tracing output will be sent to
`stderr`.
* A `$/setTrace` handler has also been added, and we also set the trace
level from the initialization options. For editors without direct
support for tracing, the environment variable `RUFF_TRACE` can override
the trace level.
* Small changes have been made to how we display tracing output. We no
longer use `tracing-tree`, and instead use
`tracing_subscriber::fmt::Layer` to format output. Thread names are now
included in traces, and I've made some adjustment to thread worker names
to be more useful.

## Test Plan

In VS Code, with `ruff.trace.server` set to its default value, no logs
from Ruff should appear.

After changing `ruff.trace.server` to either `messages` or `verbose`,
you should see log messages at `info` level or higher appear in Ruff's
output:
<img width="1005" alt="Screenshot 2024-06-10 at 10 35 04 AM"
src="https://github.com/astral-sh/ruff/assets/19577865/6050d107-9815-4bd2-96d0-e86f096a57f5">

In Helix, by default, no logs from Ruff should appear.

To set the trace level in Helix, you'll need to modify your language
configuration as follows:
```toml
[language-server.ruff]
command = "/Users/jane/astral/ruff/target/debug/ruff"
args = ["server", "--preview"]
environment = { "RUFF_TRACE" = "messages" }
```

After doing this, logs of `info` level or higher should be visible in
Helix:
<img width="1216" alt="Screenshot 2024-06-10 at 10 39 26 AM"
src="https://github.com/astral-sh/ruff/assets/19577865/8ff88692-d3f7-4fd1-941e-86fb338fcdcc">

You can use `:log-open` to quickly open the Helix log file.

In Neovim, by default, no logs from Ruff should appear.

To set the trace level in Neovim, you'll need to modify your
configuration as follows:
```lua
require('lspconfig').ruff.setup {
  cmd = {"/path/to/debug/executable", "server", "--preview"},
  cmd_env = { RUFF_TRACE = "messages" }
}
```

You should see logs appear in `:LspLog` that look like the following:
<img width="1490" alt="Screenshot 2024-06-11 at 11 24 01 AM"
src="https://github.com/astral-sh/ruff/assets/19577865/576cd5fa-03cf-477a-b879-b29a9a1200ff">

You can adjust `logLevel` and `logFile` in `settings`:
```lua
require('lspconfig').ruff.setup {
  cmd = {"/path/to/debug/executable", "server", "--preview"},
  cmd_env = { RUFF_TRACE = "messages" },
  settings = {
    logLevel = "debug",
    logFile = "your/log/file/path/log.txt"
  }
}
```

The `logLevel` and `logFile` can also be set in Helix like so:
```toml
[language-server.ruff.config.settings]
logLevel = "debug"
logFile = "your/log/file/path/log.txt"
```

Even if this log file does not exist, it should now be created and
written to after running the server:

<img width="1148" alt="Screenshot 2024-06-10 at 10 43 44 AM"
src="https://github.com/astral-sh/ruff/assets/19577865/ab533cf7-d5ac-4178-97f1-e56da17450dd">