Add maximum digit constraint for multiplication worksheets#1

ezuk wants to merge 2 commits intolewdev:masterlewdev/hw-gen:masterfrom

ezuk:claude/multiplication-generator-feature-011CUpybp35Br7rcPPgDaY5Rezuk/hw-gen:claude/multiplication-generator-feature-011CUpybp35Br7rcPPgDaY5RCopy head branch name to clipboard