Flashlight : Use udev instead of hardcoded pinephone device file

# Goal of this patch

Use udev to change or detect flash device instead of hardcoded pinephone device file.
Inspired by phosh flash manager because it works in many devices. https://gitlab.gnome.org/World/Phosh/phosh/-/blob/main/src/torch-manager.c?ref_type=heads#L168-198

# Remaining work

- [x] Minimal project for testing
- [x] Try to build for pmOS to test in my device (OP6)
- [x] Need udev rules to work (Require write permission in brightness)

# Stabilization

- [x] read permission removed in max_brightness to check if no crash
> "Failed to read max_brightness from udev device" in log
- [x] read permission removed in brightness to check if no crash
> "Failed to read brightness from udev device" in log
- [x] "Break" match in my side to check if no crash occured when no device found
> "No flashlight found" in log

# Minimal project

It run in my device perfectly, it find device, get current value and max value and toggle flashlight. It require **root** permissions to write in device file.

```cpp
#include <iostream>
#include <cstring>
#include <libudev.h>

#define TORCH_SUBSYSTEM "leds"

int main() {
    struct udev* udev = udev_new();
    struct udev_enumerate* enumerate = udev_enumerate_new(udev);

    // Use to find all devices in subsystem "leds"
    // And use match sysname to filter only flash or torch
    // Example:
    //  - /sys/devices/platform/soc@0/c440000.spmi/spmi-0/0-03/c440000.spmi:pmic@3:led-controller@d300/leds/white:flash On OP6
    //  - /sys/devices/platform/soc@0/c440000.spmi/spmi-0/0-03/c440000.spmi:pmic@3:led-controller@d300/leds/yellow:flash On OP6
    //  - /sys/devices/platform/led-controller/leds/white:flash/brightness On pinephone
    udev_enumerate_add_match_subsystem(enumerate, TORCH_SUBSYSTEM);
    udev_enumerate_add_match_sysname(enumerate, "*:torch");
    udev_enumerate_add_match_sysname(enumerate, "*:flash");
    udev_enumerate_scan_devices(enumerate);

    struct udev_list_entry *devices = udev_enumerate_get_list_entry(enumerate);
    struct udev_list_entry *entry = udev_list_entry_get_next(devices);

    if (entry == nullptr) {
        std::cout << "No flashlight found" << std::endl;
        return 1;
    }

    const char *path = udev_list_entry_get_name(entry);
    struct udev_device *torch = udev_device_new_from_syspath(udev, path);

    const char *max_brightness = udev_device_get_sysattr_value(torch, "max_brightness");

    const char *brightness = udev_device_get_sysattr_value(torch, "brightness");

    bool enabled = std::strcmp(brightness, "0") != 0;
    udev_device_set_sysattr_value(torch, "brightness", const_cast<char*>(enabled ? "0" : max_brightness));

    udev_device_unref(torch);
    udev_enumerate_unref(enumerate);
    udev_unref(udev);
    return 0;
}
```

Build with `g++ torch.cpp -ludev -o torch`
Run with `sudo ./torch`

# Important info

- **udev** dependencies added
- destructor for flashlightutil added to unref udev_device

# Require udev rules

Files `/etc/udev/rules.d/99-flashlight.rules`
```bash
# Allow everyone to set brightness of flashlight (Required for plasma-mobile flashlightplugin)
SUBSYSTEMS=="leds", KERNEL=="*:flash|*:torch", RUN+="/bin/chmod 666 %S%p/brightness"
```

pmOS : See to add depends `eudev` and makedepends `eudev-dev`