fix: Improve ZstdCompressor implementation

Signed-off-by: ddukbg <[email protected]>

lib/fluent/plugin/out_s3.rb

@@ -632,17 +632,26 @@ def compress(chunk, tmp)
     end
 
     class ZstdCompressor < Compressor
+      require 'zstd-ruby'
+
+      DEFAULT_LEVEL = 3
+
+      def initialize(level = nil)
+        @level = level || DEFAULT_LEVEL
+      end
+
       def ext
         'zst'.freeze
       end
-
+    
       def content_type
         'application/x-zst'.freeze
       end
-
+    
       def compress(chunk, tmp)
-        compressed_data = Zstd.compress(chunk.read, level: @level)
-        tmp.write(compressed_data)
+        data = chunk.read
+        compressed = Zstd.compress(data, level: @level)
+        tmp.write(compressed)
       rescue => e
         log.warn "zstd compression failed: #{e.message}"
         raise e