Fix failure to scrape magres files with more than 100 atoms

[JordD04]

CASTEP magres files store magnetic shielding information in the form:

ms O 99         -2.0523362330721022E+02          3.6848981558575366E+02         -2.2771013606692599E-02          3.5814867568808620E+02         -2.9946873927125921E+02         -1.0428524506521353E+00          7.9458932961222715E-03         -2.2003847124460636E-03         -5.5724953570109824E+02

Where O is the element and 99 is a numerical index. When that index reaches 100, the space after the O is lost, resulting in a line like:

ms O100         -2.0179072731970462E+02          3.6630064905427832E+02          1.2616916920493680E-02          3.5658185566204065E+02         -3.0353628246235576E+02         -1.0440187939142316E+00         -1.5038528456938940E-02          3.7592007872482180E-02         -5.5287819200589945E+02

Applying Python's split function to each line therefore yields:

['ms', 'O', '99', '-2.0523362330721022E+02', '3.6848981558575366E+02', '-2.2771013606692599E-02', '3.5814867568808620E+02', '-2.9946873927125921E+02', '-1.0428524506521353E+00', '7.9458932961222715E-03', '-2.2003847124460636E-03', '-5.5724953570109824E+02']
101
['ms', 'O100', '-2.0179072731970462E+02', '3.6630064905427832E+02', '1.2616916920493680E-02', '3.5658185566204065E+02', '-3.0353628246235576E+02', '-1.0440187939142316E+00', '-1.5038528456938940E-02', '3.7592007872482180E-02', '-5.5287819200589945E+02']

The second list is one element shorter, which resulted in one element of the magnetic shielding being ignored for indices above 99.
magres_scraper now takes the last 9 elements, instead of all elements after the first 3.

[codecov]

Codecov Report

Merging #197 (b9f87f6) into master (1fa94ac) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head b9f87f6 differs from pull request most recent head 66da348. Consider uploading reports for the commit 66da348 to get more accurate results

@@            Coverage Diff             @@
##           master     #197      +/-   ##
==========================================
+ Coverage   75.54%   75.56%   +0.01%     
==========================================
  Files          92       92              
  Lines       12371    12371              
==========================================
+ Hits         9346     9348       +2     
+ Misses       3025     3023       -2     

Flag	Coverage Δ
unittests	75.56% <100.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
matador/scrapers/magres_scrapers.py	95.19% <100.00%> (ø)
matador/compute/compute.py	44.38% <0.00%> (+0.21%)	⬆️

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[ml-evs]

Thanks @JordD04!