[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().

Pre-lexing a 167 KB template made of components with blocks goes from
~64 ms to ~16 ms.

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 — 1.06s wall / 1.05s CPU: https://blackfire.io/profiles/d4ce5972-9eb7-4796-beac-5f1f5921b5db/graph
• after — 72.1ms wall / 71.2ms CPU: https://blackfire.io/profiles/fe19e6f8-5d57-4d42-b270-6e741c87af20/graph
• diff: https://app.blackfire.io/profiles/compare/d4ce5972-9eb7-4796-beac-5f1f5921b5db...fe19e6f8-5d57-4d42-b270-6e741c87af20/graph

Analysis, implementation and benchmarks by Claude Opus 5.