Summary

This PR fixes the bug to avoid flattening the global-only settings for the new server.

This was added in #11497, possibly to correctly de-serialize an empty value ({}). But, this lead to a bug where the configuration under the settings key was not being read for global-only variant.

By using #[serde(default)], we ensure that the settings field in the GlobalOnly variant is optional and that an empty JSON object {} is correctly deserialized into GlobalOnly with a default ClientSettings instance.

fixes: #11507

Test Plan

Update the snapshot and existing test case. Also, verify the following settings in Neovim:

1. Nothing

ruff = {
  cmd = {
    '/Users/dhruv/work/astral/ruff/target/debug/ruff',
    'server',
    '--preview',
  },
}

2. Empty dictionary

ruff = {
  cmd = {
    '/Users/dhruv/work/astral/ruff/target/debug/ruff',
    'server',
    '--preview',
  },
  init_options = vim.empty_dict(),
}

3. Empty settings

ruff = {
  cmd = {
    '/Users/dhruv/work/astral/ruff/target/debug/ruff',
    'server',
    '--preview',
  },
  init_options = {
    settings = vim.empty_dict(),
  },
}

4. With some configuration:

ruff = {
  cmd = {
    '/Users/dhruv/work/astral/ruff/target/debug/ruff',
    'server',
    '--preview',
  },
  init_options = {
    settings = {
      configuration = '/tmp/ruff-repro/pyproject.toml',
    },
  },
}