Snapshots: formatting that hides changes (HTML, JSON-LD, JSON numbers) #116

Part of #101. Line numbers refer to branch chore/php-8.4-dependabot (#98). Verified = reproduced, suspected = from reading the code.

Fixing these changes snapshot contents. Users run UPDATE_SNAPSHOTS=1 once and review the content diffs. Do this separately from the name migration. Alternatively, make the stricter formatting opt-in.

• snapshotFormatHtml() (SnapshotTrait.php:299) runs tidy with its defaults. Verified.
  • drop-empty-elements removes <i class="icon-warning"></i>, and the test still passes.
  • Broken markup is repaired, so <p>a<p>b matches <p>a</p><p>b</p>.
  • Fragments are wrapped in <!DOCTYPE html><html><head><title></title>….
• JSON-LD turns {} into [], because snapshotFormatJsonLd() (:264) decodes with json_decode($string, true), so {"a":[]} matches a snapshot of {"a":{}}. Verified.
• JSON numbers lose precision or type, because snapshotFormatJson() (:253) has no JSON_BIGINT_AS_STRING / JSON_PRESERVE_ZERO_FRACTION. 12345678901234567890 is stored as 1.2345678901234567e+19, and 1.0 equals 1. Verified.

Breaking: snapshot contents change.