[TwigComponent] Reduce per-character work in the pre-lexer scan loops

[Kocal]

Q	A
Bug fix?	no
New feature?	no
Deprecations?	no
Documentation?	no
Issues	-
License	MIT

consumeUntilEndBlock() ran six substr() comparisons on every character of a block body, and the main loop ran a preg_match() per character to test for whitespace.

Guard the delimiter comparisons behind the only three characters that can start one ({, <, #), and swap the regex for ctype_space().

This only kicks in for templates where a component contains a traditional {% block %}; consumeUntilEndBlock() is never reached otherwise. Only 9 of this repository's 390 Twig templates match, so it doesn't move a whole-repo aggregate, but on the ones that do, the gain holds at realistic sizes too:

206 B    46.6 us -> 24.7 us
322 B    79.3 us -> 29.5 us
728 B     194 us -> 45.8 us

1.9 KB 520 us -> 92.3 us

On the synthetic 167 KB template used in the benchmark below, pre-lexing goes from ~64 ms to ~16 ms. That gain only shows up at compile time though: Twig compiles a template once and caches the result, so this is a cache-warmup and dev-loop win, not something you'll see on every request, as smnandre pointed out during review.

Benchmarked from the repository root with blackfire run symfony php bench.php:

<?php
require __DIR__.'/src/TwigComponent/vendor/autoload.php';

use Symfony\UX\TwigComponent\Twig\TwigPreLexer;

$body = str_repeat("    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>\n", 40);
$chunk = "<twig:Card>\n    {% block header %}\n{$body}\n    {% endblock %}\n</twig:Card>\n\n";

$input = str_repeat($chunk, 60); // ~167 KB
(new TwigPreLexer())->preLexComponents($input);

Blackfire:

• before (1061ms wall / 1056ms CPU): https://app.blackfire.io/envs/5f4f9a62-eaa0-45ee-b7b3-a1b879f550e9/profiles/f4c9789b-4a34-43d6-bca9-87e67832a3f0/graph
• after (73ms wall / 72ms CPU): https://app.blackfire.io/envs/5f4f9a62-eaa0-45ee-b7b3-a1b879f550e9/profiles/3d2c3cc2-f4c1-471c-aa3d-1246f8514429/graph
• diff: https://app.blackfire.io/envs/5f4f9a62-eaa0-45ee-b7b3-a1b879f550e9/profiles/compare/f4c9789b-4a34-43d6-bca9-87e67832a3f0...3d2c3cc2-f4c1-471c-aa3d-1246f8514429/graph

Analysis, implementation and benchmarks by Claude Opus 5.