[3.0][Testing] Cover four more merged fixes in the unit suite

[albertlast]

Note

This change was produced by an LLM. The tests, the commit message and this
description were all written by Claude (Anthropic), driven by @albertlast. It has
not yet had human code review.

The suite was run rather than only reasoned about, and every test below was also
run against the unfixed code it covers. Please review it as untrusted work.

Description

The second instalment of what #9326 was for, following #9511. Every bug fix merged
into release-3.0 since that sweep was looked at, including the backlog that landed
in one batch on the 29th and 30th, asking of each one whether the unit suite can
reach it and writing a test where it can.

Most of them cannot be reached: templates, JavaScript, SQL, or PHP that wants
Db::$db, User::$me, a session or a loaded theme. Four can.

Fix	What is now covered
#9484	SpoofDetector::checkReservedName() on the list as the installer writes it, plus real line breaks, homographs, entities, and the reserveWord and reserveCase settings
#9409	MessageFormatter::formatMessage() given a \Stringable, including one whose value contains MessageFormat syntax
#9453	PageIndex keeping the verdict on an out-of-bounds start through __toString()
#9440, #9442	Avatar resolving a gallery avatar, on a forum at the root of its domain and on one in a subdirectory

33 new tests and 48 new assertions, in four new files. No existing test was
touched:

File	Tests	Assertions	Covers
tests/Unit/SpoofDetectorTest.php	14	18	#9484
tests/Unit/MessageFormatterTest.php	6	6	#9409
tests/Unit/PageIndexTest.php	7	14	#9453
tests/Unit/AvatarTest.php	6	10	#9440, #9442

That takes the suite from 169 tests and 247 assertions to 202 tests and 295
assertions, still under a second.

These are regression tests, not tests written to fit

Each set was run against the code as it was before its fix, by checking out the
single source file at the commit before the merge.

• Sources/Unicode/SpoofDetector.php before [3.0] Reserve the names on the reserved names list #9484: one failure. The default list
  the installer writes has its separators spelled out as the two characters
  backslash and n, because the value travels through Table::populate() as a
  placeholder in a PHP string. Split on real newlines alone it is one long name that
  nobody would ever type, so Admin, Webmaster, Guest and root were all free
  to register on a fresh forum. The hand-edited list is the control and passes
  either side.
• Sources/Localization/MessageFormatter.php before [3.0] Keep Stringable arguments instead of dropping them #9409: three failures, all of
  them the \Stringable cases, each producing Hello {name}! — the placeholder
  shown to the member as it was written. The plain string, the number and the
  message with no placeholders pass either side. This one matters more than it
  looks: Url, IP, TimeInterval and PageIndex are all \Stringable, so any
  of them handed to Lang::getTxt() went the same way.
• Sources/PageIndex.php before [3.0] Link the first page of a topic on the message index #9453: two failures. Page 1 came out as
  <span class="current_page">1</span> instead of a link, with a next_page link
  beside it pointing at page 2 — a page index for a page you were never on. The four
  tests covering an ordinary start value pass either side, which is what makes them
  the control.
• Sources/Avatar.php before [3.0] Stop every page erroring when a member has a gallery avatar #9440: five of the six fail. The root-of-domain cases
  die with
  TypeError: preg_quote(): Argument #1 ($str) must be of type string, null given,
  which is the fatal [3.0] Stop every page erroring when a member has a gallery avatar #9440 was about; the subdirectory cases fail by falling through
  to default.png. Checked out at the commit before [3.0] Recognise a gallery avatar as a file name, not a url #9442 instead — so with [3.0] Stop every page erroring when a member has a gallery avatar #9440
  but not [3.0] Recognise a gallery avatar as a file name, not a url #9442 — four still fail, and the shape is clearer: every gallery avatar
  resolves to the default image, whichever shape the board URL has.

On the fixtures

AvatarTest looks for avatars/default.png and avatars/Oxygen/beagle.png, both
of which the repository ships. It passes id_member to the constructor, which is
the one argument that keeps it away from the attachments table, and it puts
Config::$boardurl and the three avatar settings back in tearDown().

SpoofDetectorTest covers checkReservedName() only. checkSimilarMemberName()
and checkSimilarGroupName() ask the members and membergroups tables what else
is out there and belong in the integration suite.

What is deliberately not here

The rest of the sweep. Named so the next one does not re-derive it: #9576, #9490,
#9485, #9483, #9477, #9465, #9464, #9461, #9460, #9459, #9435, #9434, #9422, #9414,
#9413, #9406, #9400 and #9380 all need a database; #9573, #9481, #9476 and #9412
need a request or a loaded theme; #9417 and #9315 are inside log(), which writes
a row; #9463 and #9348 are SQL that only one engine can disagree about; #9480 wants
a real image and GD; #9420 needs the BBCode parser, which needs both. #9402, #9418,
#9431, #9462, #9500, #9549 and #9558 are templates.

Table::populate() is the other half of #9484 and is not covered, because it
inserts rows.

Issues References (Fixes|Related|Closes)

Related to #9326, #9511, #9484, #9409, #9453, #9440, #9442.