tests: sys: Add unit test for Disjoint-set

Add unit tests for functions (`sys_set_makeset`, `sys_set_union` and `sys_set_find`).

Signed-off-by: James Roy <[email protected]>

Author: rruuaanng

tests/lib/data_structure/set/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(timespec_util)
+
+FILE(GLOB app_sources src/main.c)
+target_sources(app PRIVATE ${app_sources})

tests/lib/data_structure/set/prj.conf

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+# SPDX-License-Identifier: Apache-2.0
+
+CONFIG_ZTEST=y

tests/lib/data_structure/set/src/main.c

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+/*
+ * Copyright (c) 2025 James Roy <[email protected]>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/kernel.h>
+#include <zephyr/sys/printk.h>
+#include <zephyr/sys/set.h>
+#include <zephyr/ztest.h>
+
+struct user_data {
+	int n;
+	struct set_node ufnode;
+} data_list[5] = {{.n = 1}, {.n = 3}, {.n = 2}, {.n = 5}, {.n = 4}};
+
+ZTEST(set, test_find_and_union)
+{
+	sys_set_makeset(&data_list[0].ufnode, 5);
+	sys_set_makeset(&data_list[1].ufnode, 4);
+	sys_set_makeset(&data_list[2].ufnode, 3);
+	sys_set_makeset(&data_list[3].ufnode, 2);
+	sys_set_makeset(&data_list[4].ufnode, 1);
+
+	sys_set_union(&data_list[0].ufnode, &data_list[1].ufnode);
+	sys_set_union(&data_list[1].ufnode, &data_list[2].ufnode);
+	sys_set_union(&data_list[2].ufnode, &data_list[3].ufnode);
+	sys_set_union(&data_list[3].ufnode, &data_list[4].ufnode);
+
+	struct set_node *root_node = sys_set_find(&data_list[4].ufnode);
+	struct user_data *root_data = CONTAINER_OF(root_node, struct user_data, ufnode);
+
+	zassert_equal(root_data->n, data_list[0].n, "Root set data n are not equal");
+	zassert_equal(root_data->ufnode.rank, root_node->rank, "Root set are not equal");
+}
+
+ZTEST_SUITE(set, NULL, NULL, NULL, NULL, NULL);