Support zone-based risk in strategy validation

[sybapp]

What to build

Extend Strategy Spec validation and Nautilus evaluator replay so a Zone-Retest Entry can use a zone-based stop and an R-multiple target while retaining reverse-structure, max-bars, and RTH-flat exits.

For long entries, the initial stop should be anchored below the source zone bottom with a searched buffer in ticks, and trades whose zone-defined risk exceeds a maximum risk cap should be skipped. The target should be expressed as an R multiple of that initial risk.

Acceptance criteria

• Strategy Specs can express a zone-based long stop using source-zone bottom plus stopBufferTicks.
• Strategy Specs can express takeProfitR targets such as 1.5, 2.0, and 3.0.
• Entries whose zone-based risk exceeds the configured maximum risk cap are skipped and diagnosed or reported.
• Existing fixed-stop strategies continue to validate and replay unchanged.
• Tests cover zone stop execution, R target execution, reverse-signal exit, max-bars exit, and skipped over-risk entries.

Blocked by

• Derive zone-retest entry signals #33