Fix issue in rules matching (pre-work)

[jdromeiro]

Description

Changes to rules framework assembly necessary for fixing the rules date matching issue that will be resolved in #123 .
It includes:

• Modification of dates in RulesEngine.MatchManyAsync()
• Fix of typo in PriorityCriteria
• Replacement of explicit variables by implicit variables (var)

Change checklist

• Code follows the code rules guidelines of this project
• Commit messages follow the commit rules of this project
• I have self-reviewed my changes before submitting this pull request
• I have covered new/changed code with new tests and/or adjusted existent ones
• I have made changes necessary to update the documentation accordingly

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