Aggregated updates for the next release (0.6.9.9)

added 4 commits

• 6ad8a7fb - add method to check if a python module exist
• 73fed36f - fix caveats in various initialization of RDataFrame; fix wrong class name
• 8c4d6825 - implement various output actions for RooProcessor with interface to awkward arrays
• cb13a036 - improve stability of RooProcessor in conjunction with various RDataFrame backends

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added 1 commit

• 206d5909 - update version

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mentioned in commit 9143d459

merged