Add EncryptionBuilder.discardOutput()

Also move NullOutputStream from pgpainless-sop to pgpainless-core

pgpainless-sop/src/main/kotlin/org/pgpainless/sop/DetachedSignImpl.kt

@@ -53,15 +53,10 @@ class DetachedSignImpl : DetachedSign {
             }
         }
 
-        // When creating a detached signature, the output of the signing stream is actually
-        //  the unmodified plaintext data, so we can discard it.
-        //  The detached signature will later be retrieved from the metadata object instead.
-        val sink = NullOutputStream()
-
         try {
             val signingStream =
                 PGPainless.encryptAndOrSign()
-                    .onOutputStream(sink)
+                    .discardOutput()
                     .withOptions(ProducerOptions.sign(signingOptions).setAsciiArmor(armor))
 
             return object : ReadyWithResult<SigningResult>() {

pgpainless-sop/src/main/kotlin/org/pgpainless/sop/NullOutputStream.kt

@@ -1,31 +0,0 @@
-// SPDX-FileCopyrightText: 2024 Paul Schaub <vanitasvitae@fsfe.org>
-//
-// SPDX-License-Identifier: Apache-2.0
-
-package org.pgpainless.sop
-
-import java.io.OutputStream
-
-/** [OutputStream] that simply discards bytes written to it. */
-class NullOutputStream : OutputStream() {
-
-    override fun write(p0: Int) {
-        // nop
-    }
-
-    override fun write(b: ByteArray) {
-        // nop
-    }
-
-    override fun write(b: ByteArray, off: Int, len: Int) {
-        // nop
-    }
-
-    override fun close() {
-        // nop
-    }
-
-    override fun flush() {
-        // nop
-    }
-}