Calculate IEx table widths with Enum.reduce_while

[preciz]

Assisted-by: Codex:GPT-6
Assisted-by: Antigravity:Gemini 3.8 Flash

Calculate the maximum length directly in print_table/2 using
Enum.reduce_while/3, eliminating the intermediate lengths list and the min() call.

Bench:

# Run with: ./bin/elixir bench.exs
Mix.install([:benchee])

defmodule Baseline do
  def print_table_offset(list) do
    lengths = Enum.map(list, &String.length(&1))
    max_length = max_length(lengths)
    min(max_length, 30) + 4
  end

  defp max_length(list) do
    Enum.reduce(list, 0, &max(&1, &2))
  end
end

defmodule Proposed do
  def print_table_offset(list) do
    max_length =
      Enum.reduce_while(list, 0, fn item, acc ->
        case String.length(item) do
          len when len >= 30 -> {:halt, 30}
          len -> {:cont, max(acc, len)}
        end
      end)

    max_length + 4
  end
end

inputs = %{
  "50 items with long first item" => ["a_very_long_file_name_that_exceeds_thirty_chars.ex" | for(i <- 1..49, do: "file_#{i}.ex")],
  "50 short items (< 30 chars)" => for(i <- 1..50, do: "file_#{i}.ex")
}

Benchee.run(
  %{
    "main" => &Baseline.print_table_offset/1,
    "HEAD" => &Proposed.print_table_offset/1
  },
  inputs: inputs,
  time: 2,
  warmup: 1,
  memory_time: 1
)

Results:

Operating System: Linux
CPU Information: AMD Ryzen 7 8845HS w
Number of Available Cores: 16
Available memory: 54.72 GB
Elixir 1.21.0-dev
Erlang 29.0.5
JIT enabled: true

##### With input 50 items with long first item #####
Name           ips        average  deviation         median         99th %
HEAD        6.98 M       0.143 μs  ±1549.47%       0.130 μs        0.26 μs
main        0.22 M        4.62 μs    ±45.21%        4.42 μs        7.13 μs

Comparison: 
HEAD        6.98 M
main        0.22 M - 32.24x slower +4.47 μs

Memory usage statistics:

Name    Memory usage
HEAD         0.42 KB
main        17.62 KB - 41.76x memory usage +17.20 KB

**All measurements for memory usage were the same**

##### With input 50 short items (< 30 chars) #####
Name           ips        average  deviation         median         99th %
HEAD      222.30 K        4.50 μs   ±140.43%        4.31 μs        6.61 μs
main      217.90 K        4.59 μs   ±152.96%        4.43 μs        7.00 μs

Comparison: 
HEAD      222.30 K
main      217.90 K - 1.02x slower +0.0908 μs

Memory usage statistics:

Name    Memory usage
HEAD        18.02 KB
main        17.58 KB - 0.98x memory usage -0.43750 KB

**All measurements for memory usage were the same**

[josevalim]

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