Trim the comments added with the readuntil rewind

The floor's two reasons fit in one block, and the two tests that
restated them are named for what they cover.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hsbt

lib/net/protocol.rb

@@ -240,13 +240,10 @@ def readuntil(terminator, ignore_eof = false, limit: nil)
           if limit && rbuf_size > limit
             raise ReadLimitExceeded, "exceeded the #{limit} byte read limit"
           end
-          # Rewind by terminator.bytesize - 1 so that a terminator split
-          # across reads is not missed, however many reads it spans.
-          # @rbuf_offset is the floor for two reasons. A negative offset
-          # makes String#index search relative to the end of the buffer,
-          # skipping a match near its start. An offset below @rbuf_offset
-          # matches a terminator beginning inside bytes already returned
-          # to the caller, yielding a slice that does not end with one.
+          # Rewind so a terminator split across reads is still found. The
+          # floor guards two things. String#index reads a negative offset
+          # as counting from the end, and an offset below @rbuf_offset
+          # matches inside bytes already returned.
           offset = [@rbuf.bytesize - terminator.bytesize + 1, @rbuf_offset].max
           rbuf_fill
         end

test/net/protocol/test_protocol.rb

@@ -239,9 +239,8 @@ def test_write0_timeout_multi2
 
   class FakeReadPartialIO
     def initialize(chunks)
-      # Binary, like the bytes a real IO hands back. String#b also copies,
-      # which matters because rbuf_fill clears a string read_nonblock
-      # returns without having been handed it as the buffer.
+      # Binary, like a real IO. String#b also copies, which matters
+      # because rbuf_fill clears a string it was not handed as the buffer.
       @chunks = chunks.map(&:b)
     end
 
@@ -295,17 +294,13 @@ def test_readuntil_terminator_spanning_more_than_two_chunks # https://github.com
   def test_readuntil_clamps_a_negative_rewind # https://github.com/ruby/net-protocol/pull/66
     fake_io = FakeReadPartialIO.new(["ab\n"])
     io = Net::BufferedIO.new(fake_io)
-    # Any buffer shorter than the terminator drives the rewind below zero,
-    # and String#index reads a negative offset as counting from the end.
     assert_equal "ab", io.readuntil("ab")
   end
 
   def test_readuntil_does_not_rewind_into_consumed_bytes # https://github.com/ruby/net-protocol/pull/66
     fake_io = FakeReadPartialIO.new(["ab\r\n\r", "\nc"])
     io = Net::BufferedIO.new(fake_io)
     assert_equal "ab\r", io.readuntil("\r")
-    # The terminator is longer than what is left unconsumed, so the rewind
-    # would reach back into the bytes readuntil already returned.
     assert_raise(EOFError) { io.readuntil("\r\n\r\n") }
   end