corrected error in example 3 also in test_doc_examples.py. and correction of EUR in example 6

%% Cell type:markdown id:afb3177a698c883b tags:

This example shows how to set up the UTC properties and use them in the doublet performance calculation.

The UTC properties are used to calculate the performance of a doublet system with a heat pump.

The UTC properties modified here activate the heatpump model, the goal and return temperature of the heat network

 and the use of the Kestin viscosity model.

It also modifies the cost parameters of the heat pump, which are used to calculate the UTC cost of the system.

%% Cell type:code id:initial_id tags:

``` python

from pythermogis.aquifer import Aquifer

from pythermogis.doublet import ThermoGISDoublet

from pythermogis.settings import UTCSettings, CutoffClass

```

%% Cell type:code id:d78e3e6f8909074d tags:

``` python

aquifer = Aquifer(

    thickness=300,

    ntg=0.5,

    porosity=0.2,

    depth=2000,

    permeability=300,

)

```

%% Cell type:code id:368650bc1b5836f6 tags:

``` python

cutoff_settings = [

    CutoffClass(0,  5000, 0, 99999, 5.1), # min depth, max depth [m], min power, max power [MW], cutoff LCOE [cts/kWH]

]

```

%% Cell type:code id:59bb4943298aecec tags:

``` python

settings = UTCSettings(

    use_heatpump=True,

    goal_temperature=100,

    dh_return_temp=60,

    use_kestin_viscosity=True,

    capex_constant=0.5,

    capex_variable=1100,

    heat_exchanger_efficiency=0.4,

    heat_exchanger_parasitic=0.1,

    min_production_temp=70,

    max_cooling_temperature_range=40,

    load_hours=8760,

    cutoff_classes =cutoff_settings

)

```

%% Cell type:code id:8a75abccf9d7e13e tags:

``` python

doublet = ThermoGISDoublet(aquifer=aquifer, settings=settings)

results = doublet.simulate().to_dataset()

```

%% Cell type:code id:a01bab0bd12b4a7b tags:

``` python

print(results.data_vars.keys())

```

%% Output

    KeysView(Data variables:

        power                    float64 8B 7.527

        heat_pump_power          float64 8B 11.26

        capex                    float64 8B 21.23

        opex                     float64 8B -6.208

        utc                      float64 8B 14.31

        npv                      float64 8B -34.59

        hprod                    float64 8B 1.391e+06

        cop                      float64 8B 1.797

        power                    float64 8B 18.56

        heat_pump_power          float64 8B 11.12

        capex                    float64 8B 30.51

        opex                     float64 8B -6.85

        utc                      float64 8B 6.9

        npv                      float64 8B -16.66

        hprod                    float64 8B 3.43e+06

        cop                      float64 8B 3.843

        cophp                    float64 8B 3.254

        pres                     float64 8B 60.0

        flow_rate                float64 8B 439.2

        pres                     float64 8B 58.95

        flow_rate                float64 8B 433.4

        welld                    float64 8B 1.25e+03

        inj_temp                 float64 8B 36.65

        prd_temp                 float64 8B 75.92

        prd_temp                 float64 8B 75.91

        transmissivity_with_ntg  float64 8B 45.0

        thickness                int64 8B 300

        transmissivity           int64 8B 90000

        permeability             int64 8B 300

        temperature              float64 8B 76.65

        ntg                      float64 8B 0.5

        porosity                 float64 8B 0.2

        depth                    int64 8B 2000)

        use_kestin_viscosity=True,

        capex_constant=0.5,

        capex_variable=1100,

        heat_exchanger_efficiency=0.4,

        heat_exchanger_parasitic=0.1,

        min_production_temp=70,

        max_cooling_temperature_range=40,

        load_hours=8760,