fix(runtime): Temporal.PlainTime/PlainYearMonth/PlainMonthDay/Now test262 parity (33.6%→82.1%)

[proggeramlug]

Summary

Raises built-ins/Temporal test262 parity dramatically. The fixes split into Temporal-specific work (my assigned types) and cross-cutting fixes that lift every Temporal type (and general codegen):

Scope	Before	After	Δ
Assigned dirs (PlainTime/YearMonth/MonthDay/Now/toStringTag)	33.6% (426/1269)	86.8% (1101/1269)	+675
Full built-ins/Temporal (all 9 types)	33.1% (1525/4603)	74.9% (3449/4603)	+1924

Zero regressions across the full built-ins/Temporal suite (verified by diffing failure sets against the origin/main baseline binary), and zero non-Temporal regressions across a built-ins language shard-0/12 run. Scored Perry-only (self-validating; the Node oracle has no Temporal). Sweep jobs=16 timeout=90 on the shared Linux box (contention at higher jobs yields spurious "Wrote executable" compile-fails — all real failures are runtime-fails).

Root causes fixed

1. instanceof for Temporal values (~241) — Temporal cells are NaN-boxed with no JS class chain, so x instanceof Temporal.PlainTime was always false (every TemporalHelpers.assert* opens with it). temporal_ctor_kind (matches the ctor closure's func_ptr) wired into js_instanceof_dynamic; Temporal.X member RHS routed through the dynamic-instanceof path in HIR lowering.

2. Closure-call wrappers dropped args beyond the 5th (cross-cutting general codegen fix) — __perry_wrap_* wrappers hardcoded a 5-arg signature (stale "js_closure_call only goes up to 5" comment). Any function/method with >5 params invoked as a value or via the method-dispatch tower (obj.m(...), apply, callbacks) silently zeroed args 6+. Surfaced via assertDuration (12 params) / assertPlainTime (7). Cap raised to 16 (4 wrapper sites) + js_native_call_value's per-arity dispatch extended 8→16 (+array fallback). The dispatch tower already pads short calls to the declared arity.

3. Real Temporal.<Type>.prototype objects (~176) — prototypes were empty, so prop-desc / branding / length / name / builtin / not-a-constructor introspection all failed. Populated each prototype (all 9 types) with brand-checking accessor getters and method functions (spec .length/.name, non-constructable) sharing two generic thunks, plus @@toStringTag + constructor. Built without touching globalThis (population runs inside the singleton init where GLOBAL_THIS_READY is still false — the obvious js_function_prototype_value_for_read route deadlocks on js_get_global_this); registered in the synthetic-class-id prototype cache so new Temporal.X() doesn't overwrite it.

4. Options / coercion spec compliance (~150+, all types) — toString honors its options (calendarName / fractionalSecondDigits / smallestUnit / roundingMode, plus ZDT offset/timeZoneName and Instant timeZone) across Duration/PlainDate/PlainDateTime/PlainTime/PlainYearMonth/PlainMonthDay/ZonedDateTime/Instant; until/since/add/subtract/round/with/from parse their option bags; GetOption ToString-coerces present-but-wrong-type values (number→RangeError, Symbol→TypeError) instead of ignoring them; roundingIncrement validates NaN/Infinity/0/0.9/1e9+1; GetOptionsObject rejects primitives; ToTemporalX of a non-string primitive / Symbol / empty property bag → TypeError; non-finite numeric fields → RangeError; from() applies overflow (constrain default); YearMonth/MonthDay coerce via from_partial (monthCode support); calendar must be a string. Fixed .toString(optionsObj) mis-routing to the numeric toString(radix) path for Temporal receivers.

5. Cell immutability / getPrototypeOf — writes to a Temporal cell are no-ops (fixes segfaults from subclassing probes that did instance.constructor = …); Object.getPrototypeOf(temporalValue) returns its prototype via a per-kind class-id registry instead of derefing the cell.

Key files

• crates/perry-codegen/src/codegen/artifacts.rs (wrapper arity 5→16), expr/instance_misc1.rs, crates/perry-hir/src/lower/lower_expr.rs (instanceof routing)
• crates/perry-runtime/src/closure/dispatch.rs (arity 8→16), value/to_string.rs (radix routing), value/dyn_index.rs + object/field_set_by_name.rs (cell-write no-op), object/object_ops.rs (getPrototypeOf)
• crates/perry-runtime/src/object/{instanceof.rs, global_this.rs, temporal_proto.rs (new)}
• crates/perry-runtime/src/temporal/* (options + all type modules)

Remaining (deferred)

order-of-operations observable read-ordering; leap-second string parsing; @@toStringTag writable descriptor (pre-existing symbol-attr staleness, affects Now too); Temporal subclassing/@@species; PlainTime/YM/MD valueOf interception; a few calendar/field edge cases.