Stop using deprecated SpecialPage constructor parameters

[malberts]

Fixes #81

MediaWiki 1.46 deprecated the $restriction, $listed, $function, $file and $includable parameters of the
SpecialPage constructor. SpecialBatchUpload passed three of them, so MediaWiki emitted a deprecation warning
every time the special page was constructed.

Only the page name is passed to the parent constructor now, and the required upload right is declared by
overriding getRestriction(). Our own constructor already ignored its $name and $restriction arguments, and
$listed was only ever the default, so no caller loses anything.

getRestriction() is untyped in MediaWiki 1.43 to 1.45 and declared as : string in 1.46, so the override carries
the return type to stay compatible across the whole supported range.

Also bumps the version to 3.0.3 and records the fix in the release notes. The MediaWiki 1.46 CI job is no
longer marked experimental now that 1.46 is released, so failures against it block. Only the job tracking
MediaWiki master stays non-blocking.

Verified against a local MediaWiki 1.46 install: the new test reproduces the reported warning before the fix and
passes after it, Special:BatchUpload renders without the warning (checked with Playwright), and the page still
refuses access to users without the upload right.

_{AI-authored — Claude Code, Opus 5 (1M context); one-line ask from @malberts (the issue URL), plus a follow-up asking for the version bump; diff not yet human-reviewed; regression test seen failing then passing on a local MediaWiki 1.46 + PHP 8.3 install, before/after also checked in the browser.}