Unify and simplify JavaScript record model for user-defined indexes

[qodo-code-review]

Description

• The JavaScript record representation used in user-defined indexes had inconsistent property names and structure compared to connectors
• The evaluator was creating new function instances and record objects repeatedly, causing unnecessary allocations
• The codebase needed a cleaner separation between record mapping and expression evaluation logic

Deliverables

• Unified model: Create JsRecord class with consistent property names matching connector conventions (schema, properties, id, sequence, redacted)
• Lazy deserialization: Implement lazy-loaded Value and Properties to avoid deserializing data that may not be accessed
• Evaluator pattern: Extract evaluation logic into JsRecordEvaluator with function caching to reduce allocations
• Type conversion: Add enum-to-string converter to Jint engine for proper enum handling in JavaScript
• Documentation update: Update user-defined index documentation to reflect new record structure

[linear]

DB-1828