Improve overschrijdingsfrequenties

[veenstrajelmer]

Todo 2024:

• combined exceedance line shows odd pattern when including more data #37
• avoid RuntimeError due to nans in overschrijding #139

Todo 2025:

• Optional data corrections #29
• Exceedance frequencies for 2011 differ from reference dataset #154
• Link to Python API for HYDRA exceedance frequencies #155
• in gecombineerd line, which should be last measurement freq and first hydra freq? >> varied dependending on n-years of measurements per station before
• simplify rule_type and rule_value parameters, but keep in mind other applications
• threshold for river discharge was disabled in calc_overschrijding(). Disabling this makes it more generic and suitable for coastal stations, but it has negative impact for benedenrivierengebied stations.
• many functions are not used, sometimes because there are multiple alternatives (hkv and non-hkv). Choose which functions to keep (and increase code coverage+assertions) and remove the rest