add test fixtures for comparisons, closures, collections, default params, and more

[cs01]

Summary

• Add 8 test fixtures covering previously untested features: comparison operators, closure capture in reduce/filter, Map<string,string>, Set (skipped - native compiler bug), default function parameters, interface method dispatch, Uint8Array operations, and boolean logical operators
• Set operations test is @test-skip — native compiler generates fcmp for string pointer comparison in StringSet.has()

Test plan

• All 7 active tests pass with both JS and native compiler
• Set test skipped (native compiler StringSet.has codegen bug)
• verify:quick passes including self-hosting Stage 1