Use IO#read instead of manual readfull loop

Replace the manual `readfull` loop with Ruby's built-in `IO#read` method.
Modern Ruby (3.1+) handles non-blocking reads internally with proper
timeout support via `IO#timeout=`, making the manual loop unnecessary.

This provides ~7% performance improvement on read operations based on
benchmarks from PR #1026.

The `readfull` method is preserved in socket.rb for backwards compatibility
but is no longer used internally.

Based on work by @grcooper in PR #1026.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: petergoldstein

CHANGELOG.md

@@ -9,6 +9,7 @@ Performance:
 - Buffered I/O: Use `socket.sync = false` with explicit flush to reduce syscalls for pipelined operations
 - get_multi optimizations: Use Set for O(1) server tracking lookups
 - Raw mode optimization: Skip bitflags request in meta protocol when in raw mode (saves 2 bytes per request)
+- Use Ruby's built-in `IO#read` instead of manual `readfull` loop for improved performance on read operations (grcooper)
 
 New Features:
 

lib/dalli/protocol/connection_manager.rb

@@ -156,7 +156,7 @@ def read_line
       end
 
       def read(count)
-        @sock.readfull(count)
+        @sock.read(count)
       rescue SystemCallError, *TIMEOUT_ERRORS, *SSL_ERRORS, EOFError => e
         error_on_request!(e)
       end

test/integration/test_network.rb

@@ -198,8 +198,8 @@
 
             ssl_error = OpenSSL::SSL::SSLError.new('SSL_read: unexpected eof while reading')
 
-            # Binary protocol uses readfull for reading, meta protocol uses gets
-            stub_method = p == :binary ? :readfull : :gets
+            # Binary protocol uses read for reading, meta protocol uses gets
+            stub_method = p == :binary ? :read : :gets
             server.sock.stub(stub_method, proc { raise ssl_error }) do
               # The operation will retry with a new connection and may succeed
               # What matters is the SSLError is caught, not propagated