Skip inactive inline transforms on borrowed HTML

[dereuromark]

Outcome

Finish the post-#277 hot-loop audit by avoiding inline scans and regex calls when the corresponding Djot syntax is absent.

On the 49,540-byte carve-bench publication document, repeated isolated PHP 8.5 tracing-JIT runs land at 2.60–2.87 ms minimum (16.48–18.19 MB/s), versus 3.25 ms / 14.52 MB/s before this final pass. The fastest stable run is now effectively level with the current 18.41 MB/s carve-php reference.

How

• Return escaped plain text immediately when no inline or smart-typography marker is present.
• Skip the flat-inline parser when only smart punctuation needs rendering.
• Only run contraction, quote, and dash transforms when their trigger byte exists.
• Preserve the fail-closed path for ambiguous or unsupported syntax.

These mirror the recent carve-php architecture work: syntax-family gates, C-level bulk scans, and zero inactive extension/transform work. Djot PHP already carries the other applicable improvements: bulk inline runs, block-marker short-circuiting, renderer dispatch tables, and listener allocation avoidance.

Correctness

• Full suite: 2,819 tests, 18,472 assertions.
• Added borrowed-vs-owned parity coverage for smart punctuation.
• PHPStan and PHPCS pass.
• Publication output remains byte-identical at 98,922 bytes.

[codecov]

Codecov Report

❌ Patch coverage is 90.32258% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.19%. Comparing base (408e93c) to head (26c5255).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Performance/BorrowedHtmlLayout.php	90.32%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #278   +/-   ##
=========================================
  Coverage     92.18%   92.19%           
- Complexity     3955     3967   +12     
=========================================
  Files           111      111           
  Lines         11052    11066   +14     
=========================================
+ Hits          10188    10202   +14     
  Misses          864      864           

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