IniBasedModel should support multiple delimiters for whitespace-separated list values

[arthurvd]

Describe the bug
Some D-Flow FM MDU keywords are whitespace-separated list values and these are handled by the hydrolib.core.dflowfm.ini.util.get_split_string_on_delimiter_validator validator. This supports only one separator string, currently mostly " ".

For validating (i.e. loading) a model, we'd like to support multiple delimiters.
For serialization is OK to keep the current behavior: only one delimiter.

To Reproduce
Steps to reproduce the behavior:

1. Use unit test test_mdu_file_with_network_is_read_correctly() with test model tests/data/input/e02/c11_korte-woerden-1d/dimr_model/dflowfm/FlowFM.mdu
2. Change line

Cdbreakpoints     = 0.00063 7.23d-003

to

Cdbreakpoints     = 0.00063\t7.23d-003

(enter an actual tab character for \t)
3. Load the model
4. See validation appearing:

E               FlowFM.mdu -> wind -> CdBreakpoints -> 0
E                 value is not a valid float (type=type_error.float)

Expected behavior
For loading/validating: multiple separator strings should be possible, Multiple consecutive separators in input string should be treated as one.
For serializing, use only one separator string. Possible approach could be to allow a list of strings to be set (in get_list_delimiter()), all used by get_split_string_on_delimiter_validator for validation, and only the first list element used by _convert_value() for serialization.

Version info (please complete the following information):

• OS: N/A (tested on Windows)
• Version: 0.8.0