Perhaps you could rewrite the wait operations to await both the semaphore or cancellation token.

public async Task<bool> WaitOne(TimeSpan timeout, CancellationToken ct)
  {
    DateTime start = DateTime.UtcNow;
    while (!_semaphore.WaitOne(0))
    {
      ct.ThrowIfCancellationRequested();
      if (DateTime.UtcNow < start.Add(timeout))
        return false;
      await Task.Delay(100, ct);
    }
    return true;
  }

 public async Task<bool> WaitOne(TimeSpan timeout, CancellationToken ct)
 {
     if (WaitHandle.WaitTimeout 
         == WaitHandle.WaitAny(new[] { _semaphore, ct.WaitHandle }, timeout))
     {
         return await Task.FromResult(false);
     }
     ct.ThrowIfCancellationRequested();
     return await Task.FromResult(true);
 }

Perhaps you could rewrite the wait operations to await both the semaphore or cancellation token.

public async Task<bool> WaitOne(TimeSpan timeout, CancellationToken ct)
  {
    DateTime start = DateTime.UtcNow;
    while (!_semaphore.WaitOne(0))
    {
      ct.ThrowIfCancellationRequested();
      if (DateTime.UtcNow < start.Add(timeout))
        return false;
      await Task.Delay(100, ct);
    }
    return true;
  }

  public async Task<bool> WaitOne(TimeSpan timeout, CancellationToken ct)
  {
      var success = await Task.Run(() =>
      {
          return WaitHandle.WaitTimeout
              != WaitHandle.WaitAny(new[] { _semaphore, ct.WaitHandle }, timeout);
      });
      ct.ThrowIfCancellationRequested();
      return success;
  }