pw_stream: small fixups

Change-Id: Ifd3f25303a50d26a2c115f5a149ecaffd4d8cf7f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/18800
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Ewout van Bekkum <ewout@google.com>
diff --git a/pw_stream/public/pw_stream/memory_stream.h b/pw_stream/public/pw_stream/memory_stream.h
index c8e0460..980381a 100644
--- a/pw_stream/public/pw_stream/memory_stream.h
+++ b/pw_stream/public/pw_stream/memory_stream.h
@@ -49,7 +49,7 @@
 };
 
 template <size_t size_bytes>
-class MemoryWriterBuffer : public MemoryWriter {
+class MemoryWriterBuffer final : public MemoryWriter {
  public:
   MemoryWriterBuffer() : MemoryWriter(buffer_) {}
 
@@ -57,7 +57,7 @@
   std::array<std::byte, size_bytes> buffer_;
 };
 
-class MemoryReader : public Reader {
+class MemoryReader final : public Reader {
  public:
   MemoryReader(ConstByteSpan source) : source_(source), bytes_read_(0) {}
 
diff --git a/pw_stream/public/pw_stream/null_stream.h b/pw_stream/public/pw_stream/null_stream.h
index a039a36..b5482c3 100644
--- a/pw_stream/public/pw_stream/null_stream.h
+++ b/pw_stream/public/pw_stream/null_stream.h
@@ -24,7 +24,7 @@
 namespace pw::stream {
 
 // Stream writer which quietly drops all of the data, similar to /dev/null.
-class NullWriter : public Writer {
+class NullWriter final : public Writer {
  public:
   size_t ConservativeWriteLimit() const override {
     // In theory this can sink as much as is addressable, however this way it is
@@ -33,7 +33,7 @@
   }
 
  private:
-  Status DoWrite(ConstByteSpan data) { return Status::OK; }
+  Status DoWrite(ConstByteSpan data) override { return Status::OK; }
 };
 
 }  // namespace pw::stream