Inconsistency with Run.getProtonCharge() function in period datasets

[MialLewis]

Describe the bug

The getProtonCharge() function returns a property that does not take period filtering into account on initial load.
When filtering is applied this property is updated, accounting for period filtering AND the new filtering applied.
The proton_charge_by_period property only accounts for period filtering, not any subsequent filtering applied.

We want getProtonCharge() to be consistent in how it treats period filtering.

To Reproduce

from mantid.simpleapi import *
import matplotlib.pyplot as plt
import numpy as np

# POLREF data - so may need to call via "POLREF00043577"

test_run, test_run_monitors = Load("43577", LoadMonitors=True)



test_run_filtered = FilterByLogValue(InputWorkspace='test_run', LogName='HTS_I', MinimumValue=57.76, MaximumValue=57.79)



period_i = 0
print(test_run[period_i].getRun().getProtonCharge())
print(test_run[period_i].getRun().getProperty("proton_charge_by_period").value[period_i])
print(test_run_filtered[period_i].getRun().getProperty("proton_charge_by_period").value[period_i])
print(test_run_filtered[period_i].getRun().getProtonCharge())

Output:

40.272796630859375
20.135597229003906
20.135597229003906
18.184533727238886

Expected Output:

20.135597229003906
20.135597229003906
20.135597229003906
18.184533727238886