io/FileDescriptor: add Read()/Write() overloads with std::span

src/io/FileDescriptor.hxx

@@ -217,6 +217,10 @@ public:
 	}
 #endif
 
+	ssize_t Read(std::span<std::byte> dest) const noexcept {
+		return ::read(fd, dest.data(), dest.size());
+	}
+
 	ssize_t Read(void *buffer, std::size_t length) const noexcept {
 		return ::read(fd, buffer, length);
 	}
@@ -227,6 +231,10 @@ public:
 	 */
 	void FullRead(std::span<std::byte> dest) const;
 
+	ssize_t Write(std::span<const std::byte> src) const noexcept {
+		return ::write(fd, src.data(), src.size());
+	}
+
 	ssize_t Write(const void *buffer, std::size_t length) const noexcept {
 		return ::write(fd, buffer, length);
 	}