Add Scope plumbing and custom operator extension point

[ajpallares]

Checklist

• If applicable, unit tests
• If applicable, create follow-up issues for purchases-ios and hybrids

Motivation

Port of RevenueCat/purchases-ios#7433, the first of the rules-engine custom operator PRs. Custom rc.* operators need somewhere to live, and rc.rootVar needs the predicate's root data to survive iteration, which today is lost as soon as some / map / reduce rebind the scope to the current item.

Description

• Thread a Scope (current data plus the never-replaced root) through the evaluator instead of a bare Value, and delegate unknown operators to an empty CustomOperators dispatcher.
• Behavior-preserving: var still sees only the current item inside iteration, no fixtures were added or changed, and the pinned fixture count stays at 382.

Notes

The @Suppress("UnusedParameter") on the empty dispatcher is temporary — args and vars become used as soon as the first rc.* operator lands.

---

Note

Medium Risk
Touches the rules-engine evaluator and every operator signature, so a scope mix-up could change predicate results. Intended to be behavior-preserving for existing var/iteration semantics.

Overview
Prepares the rules engine for RevenueCat rc.* operators by replacing a bare data Value with a Scope that keeps both current data and the original root.

Iteration (some/all/none/map/filter/reduce) now rebinds only current via scoped(), so var still sees the item (or reduce’s {current, accumulator}) while custom ops can later read top-level data. Unknown operators fall through to an empty CustomOperators dispatcher (still UnsupportedOperator). firstArgEvaluated moves onto Operators.

No new operator behavior; tests wrap existing calls in Scope.

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[codecov]

Codecov Report

❌ Patch coverage is 95.65217% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.14%. Comparing base (bc89182) to head (fa1fa3c).

Files with missing lines	Patch %	Lines
.../revenuecat/purchases/rules/operators/Operators.kt	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4047      +/-   ##
==========================================
+ Coverage   83.11%   83.14%   +0.02%     
==========================================
  Files         437      439       +2     
  Lines       17930    17937       +7     
  Branches     2688     2688              
==========================================
+ Hits        14903    14913      +10     
+ Misses       2145     2143       -2     
+ Partials      882      881       -1     

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[tonidero]

Nice!