Add CyTOF workflow example

[natalie-23-gill]

Problem

CyTOF has several non-obvious requirements scattered across individual function docs:

• Data must be arcsinh-normalized and stored in the counts slot
• ndim must equal the number of markers
• Normalization is automatically skipped
• Sketching uses all features instead of variable features

Users have to piece this together from multiple ?function pages.

Proposal

Add a single end-to-end CyTOF example — either as a vignette section or as an inst/scripts/run_clustopt_cytof.R template — that consolidates all CyTOF-specific requirements and walks through the full workflow.