Variant-returning functions (hidden-dest ABI) + variant bool printing

Filed by the N-lane agent, self-resolved (sole-A confirmed this session). Functions returning Variant had NO return convention (pylib TPyList.get/pop are the first): tyVariant added to RetViaHiddenDest, so 16-byte variant results ride the same caller-owned hidden-destination path as records — every existing call/prologue/epilogue site keys on that predicate. IRLowerAddress accepts variant-returning AN_CALL/AN_VIRTUAL_CALL (the call's IR value IS the dest address), covering writeln args and assignment sources. EmitWriteVariant gains a real VT_BOOL branch: True/False (Python spelling, matches FPC's writeln(Variant-bool) rendering; old behavior printed 1/0). Stale '1' expectations updated: test_variant.pas, test_nilpy_variant, test_nilpy_local_variant. x86-64 only — cross-backend variant writers still print bools as ints (Track T will surface; noted here). Resolved with [[feature-nilpy-list]].