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»'
```

Start at the Python Descriptor constructor shown in the traceback and reproduce the supplied combo descriptor snippet. Trace how the constructor handles the descriptor string and determine whether combo descriptors are supported; done means the behavior is clarified and the issue's parsing problem is addressed or documented.

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