Historical Snapshots

• SnapshotSelectionRule
• SnapshotSelector
• MarketSnapshot
• MarketSnapshotStore

SnapshotSelectionRule	Timestamp matching: Exact, Closest, or Previous (never selects future data).
SnapshotSelector	Select one coherent historical market and calibration quote side.
MarketSnapshot	Timestamped market inputs, including curve construction configurations.
MarketSnapshotStore	Archive coherent historical markets by DateTime with JSON persistence.