BUG: Verify dynamic pressure code

[KCollins]

Validate dynamic pressure calculations.

should be: inst_val - inst_val/(min_before + min_after)

[KCollins]

Relevant code snippet - got this from Xueling:

            mom_vars = pyspedas.mms.mom(probe=[spacecraft_id.lower()], trange=[start.timestamp(), end.timestamp()],
            # mom_vars = pyspedas.mms.mom(probe=[spacecraft_id.lower()], trange=[epoch.timestamp()-5*60, epoch.timestamp()+5*60],
                                   notplot=True,no_update=False,time_clip=True)

            thx_density = mom_vars['th'+spacecraft_id.lower()+'_peem_density']
            thx_density_time = thx_density['x']
            thx_density_data = thx_density['y']

            #calculate dynamic pressure
            thx_peim_velocity = mom_vars['th'+spacecraft_id.lower()+'_peim_velocity_gse']
            thx_velocity_data = thx_peim_velocity['y']

            thx_velocity_Vx = thx_velocity_data[:,0]
            thx_velocity_Vy = thx_velocity_data[:,1]
            thx_velocity_Vz = thx_velocity_data[:,2]

            print("Computing dynamic pressure for event ", event, " out of ", len(mms_events), ".")
            thx_pdy = thx_density_data*(thx_velocity_Vx**2+thx_velocity_Vy**2+thx_velocity_Vz**2)*1.67*(10**(-6))*0.5 # should return nPa

            dyp = thx_pdy[~pd.isnull(thx_pdy)] # dynamic pressure vector without NaNs

            mms_events.loc[epoch, 'Dynamic Pressure (nPa)'] = dyp.max()
            mms_events.loc[epoch, 'Electron density'] = thx_density_data[np.argmax(dyp)]        
            mms_events.loc[epoch, 'Vx'] = thx_velocity_Vx[np.argmax(dyp)]
            mms_events.loc[epoch, 'Vy'] = thx_velocity_Vy[np.argmax(dyp)]
            mms_events.loc[epoch, 'Vz'] = thx_velocity_Vz[np.argmax(dyp)]

[KCollins]

THEMIS computations: https://doi.org/10.5281/zenodo.10531587

[KCollins]

Sanity check: Dynamic pressure should be on the order of 1-10 nPa, but could peak much higher - 100 might be reasonable. Review survey plots with Mike to confirm that the resulting estimates are in the right ballpark. Check Wang paper, Hietala, etc. as well for points of comparison.

[KCollins]

Reference: Try comparing to Fig 2 of https://angeo.copernicus.org/articles/38/287/2020/#&gid=1&pid=1