Merge bitcoin/bitcoin#28060: util: Teach AutoFile how to XOR

fa633aa690 streams: Teach AutoFile how to XOR (MarcoFalke)
000019e158 Add AutoFile::detail_fread member function (MarcoFalke)
fa7724bc9d refactor: Modernize AutoFile (MarcoFalke)
fa8d227d58 doc: Remove comments that just repeat what the code does (MarcoFalke)
fafe2ca0ce refactor: Remove redundant file check from AutoFile shift operators (MarcoFalke)
9999a49b32 Extract util::Xor, Add key_offset option, Add bench (MarcoFalke)

Pull request description:

  This allows `AutoFile` to roll an XOR pattern while reading or writing to the underlying file.

  This is needed for https://github.com/bitcoin/bitcoin/pull/28052, but can also be used in any other place.

  Also, there are tests, so I've split this up from the larger pull to make review easier, hopefully.

ACKs for top commit:
  Crypt-iQ:
    crACK fa633aa
  willcl-ark:
    Lightly tested ACK fa633aa690
  jamesob:
    reACK fa633aa690 ([`jamesob/ackr/28060.4.MarcoFalke.util_add_xorfile`](https://github.com/jamesob/bitcoin/tree/ackr/28060.4.MarcoFalke.util_add_xorfile))

Tree-SHA512: 6d66cad0a089a096d3f95e4f2b28bce80b349d4b76f53d09dc9a0bea4fc1b7c0652724469c37971ba27728c7d46398a4c1d289c252af4c0f83bb2fcbc6f8e90b

src/bench/bench.h

@@ -14,7 +14,7 @@
 #include <string>
 #include <vector>
 
-#include <bench/nanobench.h>
+#include <bench/nanobench.h> // IWYU pragma: export
 
 /*
  * Usage:

src/bench/xor.cpp

@@ -0,0 +1,24 @@
+// Copyright (c) The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://opensource.org/license/mit/.
+
+#include <bench/bench.h>
+
+#include <random.h>
+#include <streams.h>
+
+#include <cstddef>
+#include <vector>
+
+static void Xor(benchmark::Bench& bench)
+{
+    FastRandomContext frc{/*fDeterministic=*/true};
+    auto data{frc.randbytes<std::byte>(1024)};
+    auto key{frc.randbytes<std::byte>(31)};
+
+    bench.batch(data.size()).unit("byte").run([&] {
+        util::Xor(data, key);
+    });
+}
+
+BENCHMARK(Xor, benchmark::PriorityLevel::HIGH);