Add %empty branch to %loop and harden loop directives

[papac]

Summary

Adds an %empty branch to %loop, equivalent to Blade's @forelse / @empty, fixes a greedy-regex bug in %stop(...) / %jump(...), and brings the loop directives under unit tests.

%loop($users as $user)
  Hello {{ $user->name }}
%empty
  No user yet.
%endloop

What changed

%empty loop branch (src/Lexique/CompileLoop.php, src/Compiler.php)

• A bare %empty (no parentheses) between %loop and %endloop renders its content when the iterable is empty. %empty($x) with parentheses remains the existing conditional helper, even inside a loop. A bare %empty previously compiled to if (empty()), which is invalid PHP, so no working template changes meaning.
• Compilation is line by line, so %loop cannot see whether an %empty follows. A pre-scan in Compiler::compile() walks %loop / %empty / %endloop tokens with a stack after comments and verbatim blocks are stripped, and records which loops own a branch and at what depth. The three loop compilers consume those queues.
• Compiled shape, with a per-depth flag so nested loops do not clobber each other:

  <?php $__tintin_loop_1 = true; foreach ($users as $user): $__tintin_loop_1 = false; ?>
  ...
  <?php endforeach; if ($__tintin_loop_1): ?>
  ...
  <?php endif; ?>

• A %loop without %empty compiles exactly as before, so existing templates and cached output are unchanged. %for and %while have no empty branch.

Fix: greedy %stop(...) / %jump(...) condition

• The breaker regex used .+ for the condition, so %stop($b) ... ($y) on one line extended the condition to the last ) and produced broken PHP. It now uses the same balanced-paren matcher as the loop heads. Same class of bug as the condition_pattern fix already in the changelog.

Tests (tests/CompileLoopTest.php, 15 → 36 tests)

• Unit tests for every loop directive head and end variant, %stop (previously untested), %jump, the bare %empty compiler, the pre-scan (nesting, helper and stray tokens ignored, state reset), and the stack runner.
• End-to-end renders through the compiler for %loop key/value, %while, %for with %jump / %stop, and %empty with nested loops and after %stop.
• Regression test for the greedy breaker condition.

Docs (docs/en.md, docs/fr.md, CHANGELOG.md)

• New %empty section, key/value and single-line %loop examples, real %for / %while examples, note that %jump / %stop work in all loops, table of contents reordered to match, %esle → %else and %notendempty → %endnotempty typo fixes.

Verification

• vendor/bin/phpunit: 124 tests, 302 assertions, all passing.
• phpcs --standard=psr12 clean on the changed source files.
• Every documentation example rendered through Tintin::render() with both populated and empty data.