Placeholder like {name} is missing if placed at the end of sentence after transform

### Package version

_No response_

### Node version

_No response_

### Platform

_No response_

### What steps will reproduce the bug?

I encountered an issue when using `@diplodoc/transform`. If I use a placeholder like `{name}` at the end of a sentence, it disappears after running the `transform` function.

**Example input:**
```
Hello {name}
```

**Expected output:**
```

Hello {name}

```

**Actual output:**
```

Hello

```

I tried the same sample with [markdown-it](https://github.com/markdown-it/markdown-it) and there this issue does not occur — the placeholder is preserved.

**Why does this happen?**
Is this a known limitation of `@diplodoc/transform`? Could you please clarify the reason for this behavior?

**Steps to reproduce:**

```
const message = 'Hello {name}';
const result = transform(message).result.html;

console.log(result); // Output will be '

Hello

'
```

**Additional context:**

It feels like `transform` removes or mishandles such placeholders at sentence end.
Would appreciate any advice/workaround or a fix for this!

### What is the expected behavior?

```
const message = 'Hello {name}';
const result = transform(message).result.html;

console.log(result); // '

Hello {name}

'
```

### What do you see instead?

```
const message = 'Hello {name}';
const result = transform(message).result.html;

console.log(result); // '

Hello

'
```

### Additional information

_No response_