Enable parameter values for SPARQL-based Constraint Components that are not literals to be added to generated messages correctly

[mgberg]

This fixes #199. It includes two changes:

• The string representation of parameter values are used instead of trying to access the value attribute that only works for Literals.
• The regex used to find parameters is modified because the previous expression would only match one parameter substitution. If multiple were present, it would match one incorrect string. For example, if your template was {$this} does not have value {$value}, the regular expression would match $this} does not have value {$value instead of $this and $value. Note that the regex is still a bit fragile if whitespace is involved.

A test is also added to verify both these issues are resolved.

[ashleysommer]

Looks great. Thank you for the detailed issue report and clean PR with tests. Don't worry about the failing CI tests, I am working on that docker/poetry/pyducktape compilation issue.