fix(runtime): Temporal PlainDate/YearMonth/MonthDay/Time/Instant/Now tail -> ~98%

[proggeramlug]

Summary

Pushes the remaining Temporal.Plain* / Instant / Now test262 tails to ~98%, grouped by root cause, zero regressions.

Measured on the 48-core box vs node v26 (self-validating Temporal cases), built-ins/Temporal/{PlainDate,PlainYearMonth,PlainMonthDay,PlainTime,Instant,Now}, PERRY_NO_AUTO_OPTIMIZE=1 --jobs 12 (the contended default run mislabels ~66 cache/auto-opt races as compile-fail; the clean run shows the real picture):

	pass	runtime-fail	parity
before	2241	143	94.0%
after	2343	41	98.3%

+102 tests, 0 regressions.

Broad regression check — built-ins language shard 0/12 (2645 cases) diffed vs the branch base:

• Regressions (pass to fail): 0
• Fixed (fail to pass): 12 (all Temporal)

Root causes fixed (grouped)

1. from() / ToTemporalX bag reading (~40 tests). Rewrote the property-bag path for PlainDate/PlainYearMonth/PlainMonthDay/PlainTime:

• calendar slot read first, then the calendar's date fields alphabetically (day,[era,eraYear],month,monthCode,year; era/eraYear only for non-ISO calendars), then overflow last — matching the observable order-of-operations.
• monthCode now ToPrimitiveAndRequireString (was str_field, which dropped a toString-wrapped value); month/day now ToPositiveIntegerWithTruncation (a value < 1 is a RangeError even under constrain, was silently saturated to 255).
• A string item is parsed first (invalid -> RangeError) before options is validated; a wrong-typed options is a TypeError only after the fields are read. PlainMonthDay.from previously ignored options/overflow entirely.
• Non-target Temporal values (e.g. a PlainDate passed to PlainYearMonth.from) are read as property bags, not rejected.

2. Constructors (~10). PlainDate/PlainYearMonth/PlainMonthDay/PlainTime now coerce each numeric field via real ToNumber (ToIntegerWithTruncation — observes valueOf, rejects Infinity/NaN with a RangeError at the field's read position) and resolve calendar via the strict ToTemporalCalendarIdentifier. All five are now [[Construct]]-only — calling without new is a TypeError.

3. with() (~16). PlainDate/PlainYearMonth/PlainMonthDay/PlainTime with now run RejectObjectWithCalendarOrTimeZone (reads calendar+timeZone first, TypeError if present), read fields alphabetically with positive validation, and read overflow last. withCalendar() with a missing argument is a TypeError.

4. valueOf / relational (5). A statically-lowered temporal.valueOf() (lowered to DateValueOf for an any receiver) and temporal < temporal (relational ToPrimitive(number)) now route to the Temporal brand dispatch, which throws TypeError per spec.

5. Instant / Now / misc.

• Now.plainDate*ISO(tz) / PlainDate.toZonedDateTime(tz): a wrong-typed time-zone is now TypeError (was silently dropped / RangeError).
• new Temporal.Instant("abc123") -> SyntaxError; Instant.fromEpochMilliseconds -> real ToNumber (BigInt/Symbol TypeError) + NumberToBigInt integral check (RangeError).
• Instant.prototype no longer advertises the removed epochSeconds/epochMicroseconds accessors.
• PlainMonthDay.prototype.equals compares the reference (ISO) year.
• toPlainDate reads only day (YearMonth) / year (MonthDay) from its argument.

Deferred (out of scope / other workers)

• Subclassing (~31): Temporal cells have no [[Prototype]] link; full subclass support is an architectural change (also deferred by the big-3 worker).
• PlainDate.add/subtract duration-bag order-of-operations (2): lives in duration.rs (big-3 worker's domain).
• exact-multiple-of-larger-unit / float64-representable-integer (6): temporal_rs 0.2.3 rounding-precision internals.
• Instant/large-bigint (1): pre-existing BigInt unary-negation bug, outside Temporal.

Files

crates/perry-runtime/src/temporal/{options,plain_date,plain_year_month,plain_month_day,plain_time,instant,now,dispatch}.rs, object/global_this.rs, date.rs, builtins/arithmetic.rs.