size: gate Date toLocale* + Intl subclass-super behind intl-namespace (hello −99 KB, crosses under 4.1 MB)

[proggeramlug]

Fourth slice, and the largest single win of the series. #6959 gated the Intl namespace/instanceof/subclass paths, but 164 KB of the Intl web survived — ld64 -why_live pointed at two always-live references that #6959 didn't cover:

1. Date.prototype.toLocale{,Date,Time}String → date_to_locale_opts_impl → intl::temporal_locale_string. The Date prototype is installed in every binary, so its locale thunks pinned the Intl formatting machinery unconditionally.
2. The class X extends Intl.<Ctor> super probe in fetch_globals' construct path.

Both now sit behind the existing intl-namespace feature — no new feature, no new detection, because the compiler's detection already fires on every toLocale* / localeCompare / Intl token. With the feature off, the Date thunks defer to the non-locale formatter (unreachable in practice, since reaching them requires a toLocale* token that would have enabled the feature) and the Intl subclass probe can never match (no Intl constructor value can exist).

Measured: hello world 4,344,464 → 4,245,216 (−99 KB). rt::intl drops from 164 KB to near-zero for programs with no locale API.

Verification: a 9-case toLocale* probe — Date.toLocaleDateString/TimeString/String with and without options, Invalid Date, Number.toLocaleString, BigInt.toLocaleString, localeCompare, Array.prototype.toLocaleString — matches Node exactly, except German collation ("ä".localeCompare("z", "de")), which reproduces identically on released perry 0.5.1220 → pre-existing (Perry's localeCompare doesn't do CLDR collation; noted in #6960's family). Serial runtime suite 1509/1509; both feature states compile.

Series total: 4,461,216 → 4,245,216 (−216 KB, −4.8%) across #6980, #6985, #7008 and this PR.

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📥 Commits

Reviewing files that changed from the base of the PR and between c799191 and 211be53.

📒 Files selected for processing (3)

• changelog.d/7009-intl-tolocale-gate.md
• crates/perry-runtime/src/object/date_proto_thunks.rs
• crates/perry-runtime/src/object/global_this/fetch_globals.rs

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