feat(vm): Time — MRI 3.4/4.0 conformance (constructors, parts, conversions, full strftime)

[tannevaled]

Horodate: 2026-08-09 18:47 CEST

Completes the Ruby Time core class toward MRI 3.4/4.0. Time is re-backed with Go's time.Time (was go-composites/time, whole-second only) to gain nanosecond sub-second precision and fixed-offset zones — the foundation MRI-faithful Time needs. Timecop still drives Time.now through the VM clock seam (vm.nowInstant).

Implemented

Constructors — Time.new (parts, 7th-arg zone string, the 4.0 in: keyword), Time.utc/gm, Time.local/mktime (µs 7th arg), Time.at (Integer/Float/Rational/Time; subsec + :millisecond/:microsecond/:nanosecond unit and the :usec/:nsec aliases; in:), Time.now(in:). MRI field range-validation (mon/mday/hour/min/sec out of range) with overflow normalised as MRI does (Feb 30 → Mar 2, hour 24 → next day, sec 60 → next minute).

Parts — usec nsec subsec (Rational, Integer 0 on a whole second) yday utc_offset/gmt_offset/gmtoff utc?/gmt? dst?/isdst to_r, alongside the pre-existing year…sec/wday/zone/tv_*.

Conversions — utc/gmtime/localtime mutate-in-place and return self (MRI); getutc/getlocal(offset) return a new Time; round/floor/ceil(ndigits); to_a. Time − Time now returns Float seconds; +/- accept fractional seconds.

Formatting — a from-scratch strftime covering the full directive set (%Y %C %y %m %d %e %H %k %I %l %M %S %L %N %j %p %P %A %a %B %b %u %w %s %z %:z %::z %Z %U %W %G %V %n %t %% and the %c %D %F %R %r %T %x %X %h compounds) with the -_0^# flags and width; inspect renders the sub-second fraction (4.0); ctime/asctime.

Every value is asserted against real ruby 4.0.5 on fixed instants (no wall-clock/TZ dependence).

Deferred (out of core scope / gate risk)

iso8601/xmlschema/httpdate/rfc2822/rfc822 and a Time.parse/Time.strptime rewrite need the time/date stdlib parser — kept as-is (existing go-composites lenient parsers untouched). One rbgo-specific convention preserved to avoid churn: a UTC instant renders +0000 (not UTC) in to_s/inspect, matching the pre-existing Go tests.

Verification

• CI-exact whole-package coverage gate shows only the tolerated pre-existing partials — time.go is 100% (incl. every error branch).
• go test ./... exit 0; gofmt + go vet ./internal/vm/ clean.
• Fresh-binary ruby/spec ratchet: 12246 passing (language + core), up from the old floor 12068. FLOOR bumped 12068 → 12214 (N−30).

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