Template limits per article, and templates that give table rows

[bonelifer]

Two fixes from a review of the template system.

The limits now count for the whole article. The limits of 2000 calls and functions and 500 template calls were reset at each template call, so an article with many calls could do a full render for each. They now count for the whole article, there is a 500,000-character output budget, and once a limit is used up the remaining calls are answered with a "Too many templates" message without rendering anything. A page with 1500 calls of a nested template went from 1.6 s to 0.24 s. #ifexist answers are also kept for the request, so repeated checks do not repeat the query.

Templates can give table rows and cells. <table>{{Row|a|1}}{{Row|b|2}}</table> left the braces as text, because the placeholder for a call was a <span>, which cannot sit between table tags. It is now a <template> element, which can. A template whose text starts with <tr>, <tbody>, <td> and so on is parsed inside a table that is then taken off, since rows do not parse on their own. A new migration clears the cached text formatter configuration so existing boards pick up the new tag.

Measured (MySQL 8.0 board): about 1 ms for each template call written in an article, and one extra query for the template pages however many calls there are. A cache of rendered articles is still not needed; the TODO plan has the numbers.

Docs. README: template rows and the limits. TODO plan: the measurements.

Tests

• Unit tests: 220 tests, 511 assertions, all pass, including the fan-out, the per-article counting and the table wrapper.
• Two new browser tests pass 6 of 6 on phpBB 3.3.19 with SQLite, 4.0.0-a3-dev with SQLite, MySQL 8.0 and PostgreSQL 16: rows and cells from templates, and abuse (fan-out, 1500 calls, 700 calls to one template, #expr and date abuse, loops) with a time limit.
• The template, parser function, table and headings browser tests still pass on all four boards.

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Investigated and written by Claude on behalf of William Jacoby (bonelifer).