Decrease RAM usage of RMtools (#109)

* Decrease RAM usage of RMtools

This decreases the peak RAM usage by about 40-50 percent when write_separate_RMSF=True as we don't need to keep everything in memory.
Additionally, it creates the option to do the RM synthesis and RMSF calculation separately instead of in the same function which decreases the RAM usage of the POSSUM Polarimetry pipeline by about 20-25 percent throughout, while not losing any noticable CPU time.
To make this change, I did have to make sure lambda0Sq_m2 is reported by util_RM.py and handled correctly by both do_RMsynth_1D and do_RMsynth_3D.
---------
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Alec Thomson (S&A, Kensington WA) <[email protected]>
Co-authored-by: Cameron Van Eck <[email protected]>

.github/workflows/python-package.yml

@@ -37,5 +37,4 @@ jobs:
     - name: Test with pytest
       shell: bash -l {0}
       run: |
-        cd tests/
-        pytest *.py
+        pytest

RMtools_1D/do_RMsynth_1D.py

@@ -324,7 +324,7 @@ def run_rmsynth(
     )
 
     # Calculate the Rotation Measure Spread Function
-    RMSFArr, phi2Arr_radm2, fwhmRMSFArr, fitStatArr = get_rmsf_planes(
+    RMSFArr, phi2Arr_radm2, fwhmRMSFArr, fitStatArr, _ = get_rmsf_planes(
         lambdaSqArr_m2=lambdaSqArr_m2,
         phiArr_radm2=phiArr_radm2,
         weightArr=weightArr,