Fetched_constraints is a class of argopy.utils.format.UriCName cannot directly save to netcdf

[cywhale]

Reproducible code:

ds = DataFetcher().float(5903377).to_xarray()
ds
ds.to_netcdf("./argo_data.nc")

Error message
File ~/.pyenv/versions/py312numpy1/lib/python3.12/site-packages/xarray/backends/api.py:1292, in to_netcdf(dataset, path_or_file, mode, format, group, engine, encoding, unlimited_dims, compute, multifile, invalid_netcdf)
1290 # validate Dataset keys, DataArray names, and attr keys/values
1291 _validate_dataset_names(dataset)
...
197 "netCDF files, its value must be of one of the following types: "
198 f"{', '.join([vtype.name for vtype in valid_types])}"
199 )

TypeError: Invalid value for attr 'Fetched_constraints': WMO5903377. For serialization to netCDF files, its value must be of one of the following types: str, Number, ndarray, number, list, tuple

Debugging:

for attr, value in ds.attrs.items():
    print(f"{attr}: {type(value)}")
    if not isinstance(value, (str, int, float, list, tuple, np.ndarray)):
        print(f"Converting {attr} to string")
        ds.attrs[attr] = str(value)  # Convert unsupported types to string

ds.to_netcdf("../tmp/argo_data.nc")

Fetched_constraints: <class 'argopy.utils.format.UriCName'>
Converting Fetched_constraints to string

and then save done

Problem Description

I think it come from
#400

ds.attrs["Fetched_constraints"] = UriCName(url).cname

Versions

Output of `argopy.show_versions()`

SYSTEM

commit: None
python: 3.12.5 (main, Sep 2 2024, 14:21:15) [GCC 13.2.0]
python-bits: 64
OS: Linux
OS-release: 6.8.0-45-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: zh_TW.UTF-8
LOCALE: zh_TW.UTF-8
libhdf5: 1.14.2
libnetcdf: 4.9.3-development

INSTALLED VERSIONS: CORE

aiohttp : 3.10.5
argopy : 1.0.0
decorator : 5.1.1
erddapy : 2.2.0
fsspec : 2023.10.0
netCDF4 : 1.7.1.post2
...

INSTALLED VERSIONS: PIP