Audit \dontrun{} usage and add missing examples to reference docs

[danmcgraw94]

Several reference pages show ## Not run: with no explanation, and other pages are missing examples entirely.

\dontrun{} audit

Currently used on: bootstrap_vfc, flow_frequency_sampler_expected, hydrograph_setup, rfa_simulate, stage2aep, aep2stag.

• Remove \dontrun{} from fast functions where it isn't needed (likely hydrograph_setup, aep2stag)
• Keep \dontrun{} on genuinely slow/resource-intensive functions (rfa_simulate, possibly bootstrap_vfc)
• Add a brief comment inside remaining \dontrun{} blocks explaining why (e.g., "not run automatically due to long computation time")

Missing examples

• interpolate_aep_matrix
• interpolate_stage_matrix
• stage2aep
• stage_frequency_curve
• rfa_simulate (check that pkgdown still renders the \dontrun{} code block)
• theme_rfar_conceptual — reference page renders blank; investigate roxygen block
• Dataset docs (jmd_hydro_*, jmd_resmodel) — consider adding minimal examples like str(jmd_hydro_apr1999) or head(...)

Feedback source

Raised by Sadie.