Add ScoringRules.jl as scoring backend

[jc-macdonald]

Summary

The scoring module is being developed as a standalone package at jcm-sci/ScoringRules.jl since proper scoring rules have broad utility beyond model criticism.

TradeStudy.jl should depend on ScoringRules.jl and wire it into the AbstractScorer dispatch system from the Protocols module (#25).

Proposed Design

struct ProperScoringRuleScorer <: AbstractScorer
    metric::Symbol  # :crps, :energy, :wis, :brier, etc.
end

function score(s::ProperScoringRuleScorer, obs, pred)
    ScoringRules.score(s.metric, obs, pred)
end

Depends On

• Scaffold Protocols module: abstract types and core structs #25 (Protocols module)
• jcm-sci/ScoringRules.jl reaching a usable state

Acceptance Criteria

• ScoringRules added to [deps] in Project.toml
• ProperScoringRuleScorer exported and documented
• Integration test using CRPS on synthetic data