test: add Rhythm Palette Tests Extended

Adds 'Rhythm Palette Tests Extended' (29 blocks) testing additional rhythm
blocks: multiplybeatfactor, skipnotes, and rhythmicdot2 in combination.

Supplements master's existing Rhythm Palette Tests Beginner and Advanced
with blocks not covered there. Removed redundant Beginner action as master
already has comprehensive 192-block version with assertions.

Follows naming convention from PR sugarlabs#5747. Rebased on current master (938a676).
Total blocks: 694 -> 724 (29 new blocks + 1 nameddo call).

Author: Ashutoshx7