Use constants for parameter names and remove trivial reader functions

[github-actions]

This is an automatic cherry-pick of 77108503a07ae50a3503eaac83b043ba5d6629bc

The original PR was #172 with message:

Defining string literals in a single place reduces the risk of spelling mistakes.

The functions for reading parameter values will never fail, so checking return values is pointless.

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• I have added tests that prove my fix is effective or that my feature works
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• I have made corresponding changes to the documentation