[df] Allow reading std::array branches from TTree

[vepadulano]

Add a specialization of RTreeColumnReader that reads values from a branch of type std::array. The specialization uses the non-adopting view from RVec to expose the contents of the array to nodes of the graph.

Fixes #16160

[github-actions[bot]]

Test Results

    13 files      13 suites   2d 17h 46m 24s :stopwatch:  3 025 tests  3 025 :white_check_mark: 0 :zzz: 0 :x: 33 788 runs  33 788 :white_check_mark: 0 :zzz: 0 :x:

Results for commit 8515c34e.

:recycle: This comment has been updated with latest results.