This function uses `readers.utils.generic_open()` and `np.frombuffer()` to achieve this.

In particular, the following functions/methods have been modified:
- `has_archive_header()` now uses `readers.utils.generic_open()` instead of `open()`.
- `read_header()` now uses `readers.utils.fromfile()` instead of `np.formfile()`.
- `NativeMSGFileHandler._read_trailer()` now uses `readers.utils.fromfile()` instead of `np.formfile()`.
- `NativeMSGFileHandler._get_memmap()` has been renamed to `NativeMSGFileHandler._get_array()` and now uses `readers.utils.fromfile()` instead of `np.memmap()`.

Reason: since `NativeMSGFileHandler._get_memmap()` has been renamed to `NativeMSGFileHandler._get_array()`.

…n `seviri_l1b_native`

This includes generating an actual file on disk and attempt to read it.

… well as plain files

…le()`

This concerns `test_read_physical_seviri_nat_file()`.

This is to ensure that the remote reading tests can also run on Windows.
Note: `fsspec` expects a POSIX path.

…unknown marks

We do not need these marks anymore, as we decreased the size of the generated seviri native file. As a result, the tests now run fast enough.

This warning is totally benign. It is caused as a result of the seviri native file that we create which is essentially filled with zeros.

The issue was an unexpected indentation on the last line of the docstring!

…readers table

This includes:
- Extracting the `_get_array()` method so that it is now a function in the module and not a class method.
- Introduction of `NativeMSGFileHandler_make_dask_array_with_map_blocks()` method to utilize the dask `map_blocks()`.
- Introduction of a new method, namely `NativeMSGFileHandler._number_of_visir_channels` to facilitate testing and mock patching.
- Adapting the mock patches in tests accordingly.

…array

…rint?)