Brummel
cf102172ec
Foundation for `aura sweep|walkforward --real` (#106, plan 0060 Task 1). - New CLI-side `DataChoice` (parsed) / `DataSource` (opened) provider: the synthetic-vs-real source choice as one type, supplying a member's source, pip, full/windowed sources, and walk-forward roller sizes. Not yet wired into the family builders (plan Tasks 2-5); `#[allow(dead_code)]` marks the wired-later items, to be removed once the builders thread `&DataSource`. - DRY: `run_sample_real`'s inline pip-refusal / no-data refusal / probe-window logic is extracted to shared `instrument_spec_or_refuse` / `no_real_data` / `probe_window` helpers, now reused by `DataSource::from_choice` / `full_window` instead of duplicated. - Real walk-forward roller-size constants (90d / 30d / 30d in ns, Fork D/F). The synthetic provider is consumer-dependent by design (full-window consumers draw showcase_prices; windowed consumers draw walkforward_prices) so the byte-unchanged guarantee holds across both family paths. Verified: cargo test -p aura-cli (all green incl. byte-unchanged synthetic path), cargo clippy -p aura-cli --all-targets -D warnings (clean). Full-workspace gate at iter close after Tasks 2-5. refs #106