feat: support PID iteration

This change introduces the `lwp_pid_for_each` function, which provides a
convenient and thread-safe method for iterating over PIDs with a user-
defined callback. This addition is necessary to support cases where
operations must be performed on each PID in the balanced tree, enhancing
flexibility and modularity for PID management.

Changes:
- Added `lwp_pid_for_each` function in `lwp_pid.c` to allow iteration
  over PIDs using a callback function and optional data parameter.
- Defined a new internal `pid_foreach_param` structure to encapsulate
  the callback and data for the iteration.
- Added `_before_cb` helper function for executing the callback on each
  PID node during AVL traversal.
- Ensured thread safety by acquiring and releasing the PID lock around
  the AVL traversal within `lwp_pid_for_each`.
- Updated `lwp_pid.h` with the `lwp_pid_for_each` function prototype and
  included `rtthread.h` for necessary types.

Signed-off-by: Shell <smokewood@qq.com>

components/lwp/lwp_pid.h

@@ -15,6 +15,8 @@
 extern "C" {
 #endif
 
+#include <rtthread.h>
+
 #define LWP_CREATE_FLAG_NONE         0x0000
 #define LWP_CREATE_FLAG_ALLOC_PID    0x0001  /* allocate pid on lwp object create */
 #define LWP_CREATE_FLAG_INIT_USPACE  0x0002  /* do user space initialization */
@@ -24,6 +26,8 @@ struct rt_lwp;
 
 struct lwp_avl_struct *lwp_get_pid_ary(void);
 int lwp_pid_init(void);
+
+int lwp_pid_for_each(int (*cb)(pid_t pid, void *data), void *data);
 void lwp_pid_put(struct rt_lwp *lwp);
 void lwp_pid_lock_take(void);
 void lwp_pid_lock_release(void);