tests: lib: json: zero-initialize structs before using memcmp in tests

Zero-initialize the `test_int_limits` and `test_enums` structs before
assignment and decoding in their respective tests.

This ensures that all padding bytes are set to zero, making
`memcmp`-based comparisons reliable and portable across different
architectures and compilers.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

Author: kartben

tests/lib/json/src/main.c

@@ -596,35 +596,35 @@ ZTEST(lib_json_test, test_json_limits)
 			 "\"uint8_min\":0"
 			 "}";
 
-	struct test_int_limits limits = {
-		.int_max = INT_MAX,
-		.int_cero = 0,
-		.int_min = INT_MIN,
-		.int64_max = INT64_MAX,
-		.int64_cero = 0,
-		.int64_min = INT64_MIN,
-		.uint64_max = UINT64_MAX,
-		.uint64_cero = 0,
-		.uint64_min = 0,
-		.uint32_max = UINT32_MAX,
-		.uint32_cero = 0,
-		.uint32_min = 0,
-		.int16_max = INT16_MAX,
-		.int16_cero = 0,
-		.int16_min = INT16_MIN,
-		.uint16_max = UINT16_MAX,
-		.uint16_cero = 0,
-		.uint16_min = 0,
-		.int8_max = INT8_MAX,
-		.int8_cero = 0,
-		.int8_min = INT8_MIN,
-		.uint8_max = UINT8_MAX,
-		.uint8_cero = 0,
-		.uint8_min = 0,
-	};
+	struct test_int_limits limits = {0};
+	struct test_int_limits limits_decoded = {0};
+
+	limits.int_max = INT_MAX;
+	limits.int_cero = 0;
+	limits.int_min = INT_MIN;
+	limits.int64_max = INT64_MAX;
+	limits.int64_cero = 0;
+	limits.int64_min = INT64_MIN;
+	limits.uint64_max = UINT64_MAX;
+	limits.uint64_cero = 0;
+	limits.uint64_min = 0;
+	limits.uint32_max = UINT32_MAX;
+	limits.uint32_cero = 0;
+	limits.uint32_min = 0;
+	limits.int16_max = INT16_MAX;
+	limits.int16_cero = 0;
+	limits.int16_min = INT16_MIN;
+	limits.uint16_max = UINT16_MAX;
+	limits.uint16_cero = 0;
+	limits.uint16_min = 0;
+	limits.int8_max = INT8_MAX;
+	limits.int8_cero = 0;
+	limits.int8_min = INT8_MIN;
+	limits.uint8_max = UINT8_MAX;
+	limits.uint8_cero = 0;
+	limits.uint8_min = 0;
 
 	char buffer[sizeof(encoded)];
-	struct test_int_limits limits_decoded = {0};
 
 	ret = json_obj_encode_buf(obj_limits_descr, ARRAY_SIZE(obj_limits_descr),
 				&limits, buffer, sizeof(buffer));
@@ -2156,18 +2156,16 @@ ZTEST(lib_json_test, test_json_enums)
 			 "\"i32\":-2147483648,"
 			 "\"u32\":4294967295"
 			 "}";
-
-	struct test_enums enums = {
-		.i8 = I8_MIN,
-		.u8 = U8_MAX,
-		.i16 = I16_MIN,
-		.u16 = U16_MAX,
-		.i32 = I32_MIN,
-		.u32 = U32_MAX,
-	};
-
 	char buffer[sizeof(encoded)];
 	struct test_enums enums_decoded = {0};
+	struct test_enums enums = {0};
+
+	enums.i8 = I8_MIN;
+	enums.u8 = U8_MAX;
+	enums.i16 = I16_MIN;
+	enums.u16 = U16_MAX;
+	enums.i32 = I32_MIN;
+	enums.u32 = U32_MAX;
 
 	ret = json_obj_encode_buf(enums_descr, ARRAY_SIZE(enums_descr),
 				&enums, buffer, sizeof(buffer));