Add CSV::TSV class for tab-separated values (#319)

GitHub: fix GH-272

This adds `CSV::TSV` that uses `\t` as the default column separator.

How to use:

```ruby
require "csv"

# Read TSV file with default tab separator
CSV::TSV.read("data.tsv")

# Parse TSV string
CSV::TSV.parse("a\tb\tc")

# Generate TSV content
CSV::TSV.generate do |tsv|
  tsv << ["a", "b", "c"]
  tsv << [1, 2, 3]
end
```

Reported by kojix2. Thanks!!!

---------

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

lib/csv.rb

@@ -2129,6 +2129,12 @@ def initialize(data,
     writer if @writer_options[:write_headers]
   end
 
+  class TSV < CSV
+    def initialize(data, **options)
+      super(data, **({col_sep: "\t"}.merge(options)))
+    end
+  end
+
   # :call-seq:
   #   csv.col_sep -> string
   #

test/csv/test_tsv.rb

@@ -0,0 +1,32 @@
+require_relative "helper"
+
+class TestTSV < Test::Unit::TestCase
+  def test_default_separator
+    tsv = CSV::TSV.new(String.new)
+    assert_equal("\t", tsv.col_sep)
+  end
+
+  def test_override_separator
+    tsv = CSV::TSV.new(String.new, col_sep: ",")
+    assert_equal(",", tsv.col_sep)
+  end
+
+  def test_read_tsv_data
+    data = "a\tb\tc\n1\t2\t3"
+    result = CSV::TSV.parse(data)
+    assert_equal([["a", "b", "c"], ["1", "2", "3"]], result.to_a)
+  end
+
+  def test_write_tsv_data
+    output = String.new
+    CSV::TSV.generate(output) do |tsv|
+      tsv << ["a", "b", "c"]
+      tsv << ["1", "2", "3"]
+    end
+    assert_equal("a\tb\tc\n1\t2\t3\n", output)
+  end
+
+  def test_inheritance
+    assert_kind_of(CSV, CSV::TSV.new(String.new))
+  end
+end