stream: Make capability device IDs an JSON object

Also change the encoding of the byte array to use hexadecimal encoding,
i.e. the byte array [100, 200] in becomes "64c8".

src/examples/utils.h

@@ -0,0 +1,60 @@
+/* PipeWire */
+/* SPDX-FileCopyrightText: Copyright © 2026 Red Hat */
+/* SPDX-License-Identifier: MIT */
+
+static inline char *
+encode_hex(const uint8_t *data, size_t size)
+{
+	FILE *ms;
+	char *encoded = NULL;
+	size_t encoded_size = 0;
+	size_t i;
+
+	ms = open_memstream(&encoded, &encoded_size);
+	for (i = 0; i < size; i++) {
+		fprintf(ms, "%02x", data[i]);
+	}
+	fclose(ms);
+
+	return encoded;
+}
+
+static inline int8_t
+ascii_hex_to_hex(uint8_t ascii_hex)
+{
+	if (ascii_hex >= '0' && ascii_hex <= '9')
+		return ascii_hex - '0';
+	else if (ascii_hex >= 'a' && ascii_hex <= 'f')
+		return ascii_hex - 'a' + 10;
+	else if (ascii_hex >= 'A' && ascii_hex <= 'F')
+		return ascii_hex - 'A' + 10;
+	else
+		return -1;
+}
+
+static inline int
+decode_hex(const char *encoded, uint8_t *data, size_t size)
+{
+	size_t length;
+	size_t i;
+
+	length = strlen(encoded);
+
+	if (size < (length / 2) * sizeof(uint8_t))
+		return -1;
+
+	i = 0;
+	while (i < length) {
+		int8_t top = ascii_hex_to_hex(encoded[i]);
+		int8_t bottom = ascii_hex_to_hex(encoded[i + 1]);
+
+		if (top == -1 || bottom == -1)
+			return -1;
+
+		uint8_t el = top << 4 | bottom;
+		data[i / 2] = el;
+		i += 2;
+	}
+
+	return 1;
+}