extract the year from source

[Shirazos7]

Changes:

• writing a new function in getAsXml to extract the year of source from the articles of the softwares
• adding the source_year node in plain_with_references for testing and also to show the result of the extraction

[Shirazos7]

in the first two commits
[349ca7e]
[940bd39]

you will notice the main work done
the following commits were an attempt to fix the issues that i faced with deep source
however there is only one issue that he is showing me , therefore i wanted you to see if you could actually solve it.

@Mazztok45

[Mazztok45]

https://app.deepsource.com/gh/MaRDI4NFDI/python-zbMathRest2Oai/run/a7de6fe8-57fd-4aa5-b7f4-4d26e7eed50f/python/PY-R1000?listcategory&listsort&listq&listindex=0

@Shirazos7
The cyclomatic complexity issue is now fixed.