Add Scenario management

[pplonski]

Add scenario support to Mercury for what-if analysis.

Expected use case

A user wants to save several versions of an analysis, for example:

• Baseline
• High growth
• Low price

Each scenario contains:

• scenario name
• inputs
• outputs

User can later load or compare saved scenarios.

V1

Add:

• Save scenario button
• ask for scenario name
• save provided inputs
• save provided outputs
• scenario selector
• Compare button showing scenarios side by side

Possible API:

mr.Scenarios(
    inputs={
        "Growth": growth,
        "Price": price,
    },
    outputs={
        "Revenue": revenue,
        "Profit": profit,
    },
)

Example comparison:

              Baseline   High growth
Growth            5%          15%
Price            $50          $50
Revenue         $4.1M        $5.2M
Profit          $1.2M        $1.6M