Error parsing combo descriptor

When initialising a `combo` descriptor this error was raised:

bdkpython.bdk.DescriptorError.Miniscript: error_message='unexpected «combo(1 args) while parsing Miniscript»'

Is this a legitimate error with the descriptor?

#### Code

```python
from bdkpython.bdk import Descriptor, Network

TEST_NETWORK = Network(1)
DESC = "combo(tpubD6NzVbkrYhZ4YSPGUiT67AZRVmJUjPn1Twt4JuYPrkGZiwVKyBofjVRej8A194X2X4Toyo22HSaJJYLH2g4gd2JGnztsKzShiRFwWgAYi5D/0h/0h/*h)#leqp7cnz"

my_desc = Descriptor(descriptor=DESC, network=TEST_NETWORK)
```

#### Traceback

```bash
Traceback (most recent call last):
File "/Users/s/projects/bdk_playground/check.py", line 9, in
my_desc = Descriptor(descriptor=DESC, network=TEST_NETWORK)
File "/Users/s/projects/bdk_playground/env/lib/python3.10/site-packages/bdkpython/bdk.py", line 17768, in __init__
self._pointer = _uniffi_rust_call_with_error(_UniffiConverterTypeDescriptorError,_UniffiLib.uniffi_bdkffi_fn_constructor_descriptor_new,
File "/Users/s/projects/bdk_playground/env/lib/python3.10/site-packages/bdkpython/bdk.py", line 295, in _uniffi_rust_call_with_error
_uniffi_check_call_status(error_ffi_converter, call_status)
File "/Users/s/projects/bdk_playground/env/lib/python3.10/site-packages/bdkpython/bdk.py", line 306, in _uniffi_check_call_status
raise error_ffi_converter.lift(call_status.error_buf)
bdkpython.bdk.DescriptorError.Miniscript: error_message='unexpected «combo(1 args) while parsing Miniscript»'
```

从回溯中显示的 Python Descriptor 构造函数开始，复现提供的 combo descriptor 代码片段。跟踪构造函数如何处理 descriptor 字符串，并确定是否支持 combo descriptor；当行为得到澄清且 issue 的 parsing 问题得到解决或记录后，即视为完成。

由索引模型根据 Issue 内容生成。