fix: check current state before toggling on Windows

[fasuizu-br]

Summary

Closes #13

The set() method unconditionally sent a key press + release via keybd_event, which always toggled the lock key regardless of the requested state. The state parameter was completely ignored.

This meant:

• enable() could turn a key OFF if it was already ON
• disable() could turn a key ON if it was already OFF
• set(key, Enabled) on an already-enabled key would disable it

Fix

Read the current state via GetKeyState before acting. Only send the toggle key event when the current state differs from the desired one — making set() idempotent, matching the behavior on macOS (IOHIDSetModifierLockState) and Linux (XkbLockModifiers).

Before

fn set(&self, key: LockKeys, state: LockKeyState) -> LockKeyResult {
    unsafe {
        let key = lock_key_to_vkkey!(key) as BYTE;
        keybd_event(key, 0x45, KEYEVENTF_EXTENDEDKEY | 0, 0);
        keybd_event(key, 0x45, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
    }
    Ok(state) // state was never checked
}

After

fn set(&self, key: LockKeys, state: LockKeyState) -> LockKeyResult {
    let current = self.state(key)?;
    if current != state {
        unsafe {
            let key = lock_key_to_vkkey!(key) as BYTE;
            keybd_event(key, 0x45, KEYEVENTF_EXTENDEDKEY | 0, 0);
            keybd_event(key, 0x45, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
        }
    }
    Ok(state)
}

Test plan

• cargo check passes (macOS — Windows code behind cfg(windows))
• Manual: on Windows, LockKey::new().enable(CapitalLock) when CapsLock is already ON → stays ON (no toggle)
• Manual: LockKey::new().disable(CapitalLock) when CapsLock is already OFF → stays OFF (no toggle)