Make array literal registry lazy on NaturalArray and expand PTAC native execution coverage

[Copilot]

This PR addresses four gaps: array literal methods were eagerly materializing NaturalArray, PTAC still fell back frequently to the interpreter, code needed cleanup in touched paths, and an issue report artifact was requested.
The changes make NaturalArray method dispatch lazy/streamed where appropriate, broaden native PTAC opcode execution, and add a root-level issue report file summarizing findings and follow-ups.

• Array literal registry: remove eager NaturalArray materialization

  • LiteralRegistry now treats NaturalArray separately from concrete List inputs.
  • map/filter on NaturalArray return lazy AbstractList views instead of forcing toList().
  • reduce on NaturalArray iterates by index (size() + get(i)) without pre-copying the full array.
  • Added clearer limit errors when operations exceed Integer.MAX_VALUE.

• PTAC executor: reduce interpreter fallback surface

  • Added instruction-pointer execution with label indexing for branch flow.
  • Native support added for:
    • control flow: NOP, BRANCH, BRANCH_IF
    • lazy ops: LAZY_GET, LAZY_SET, LAZY_SIZE, LAZY_COMMIT
    • pattern ops: MAP, FILTER, REDUCE, FILTER_MAP
  • Kept recursive/closure-sensitive opcodes on fallback path where parity risk is higher.

• Complexity validation runner (problem-specific)

  • Added ArrayLiteralRegistryComplexityRunner to compare eager-vs-lazy behavior across increasing sizes and verify size-independent setup characteristics for lazy map/filter.

• Issue report submission artifact

  • Added root file ISSUE_REPORT_PTAC_NATURALARRAY.md with:
    • what changed,
    • remaining fallback areas,
    • follow-up issue recommendations.

// Before (NaturalArray path forced eager copy)
List<Object> source = arr.toList();

// After (NaturalArray map/filter path returns lazy view)
return new LazyNaturalArrayMapView(naturalArray, new NaturalArrayMapper() {
    @Override
    public Object map(long index, Object value) {
        return applyOperator(typeHandler, value, op, operand);
    }
});