@spec diff(%{required(String.t()) => term()}, String.t()) ::
  {[String.t()], [String.t()]}

Compare installed packages against the lockfile.

Returns {missing, extra} where:

• missing — packages in lockfile but not in node_modules
• extra — packages in node_modules but not in lockfile

@spec disk_size(String.t()) :: non_neg_integer()

Get the total disk size of node_modules in bytes.

@spec file_count(String.t()) :: non_neg_integer()

Count the total number of files in node_modules.

@spec installed(String.t()) :: [String.t()]

List all installed packages in node_modules.

Returns a sorted list of package names (including scoped).

@spec version(String.t(), String.t()) :: String.t() | nil

Get the installed version of a package by reading its package.json.