Bugfix/fix potential security vulnerability

[mgovers]

Fixes #200

Changes proposed in this PR include:

• Do not use regex for the node ref parsing (i.e. matching whether an attribute string matches "node", "from_node", "to_node", ... (original regex may result in exponential blowup when input string size increases => DoS attacks)
• For consistency: rewrite all other regex patterns to python functions that call the regex
• Cleanup code that can be written in a more readable way because of the above change

Could you please pay extra attention to the points below when reviewing the PR:

• Sonar cloud should not report the security vulnerability anymore after this change

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

100.0% Coverage
0.0% Duplication