Perf: hoist loop-invariant option getters out of the main loop

[mmucklo]

Profile-driven follow-up to the mb_str_split change (#60). An Xdebug profile showed the remaining cost concentrated in the state-machine loop body, with ParseOptions getters (getSeparators 1.5%, getBannedChars, getUseWhitespaceAsSeparator) called inside the per-character loop.

Change

Those three getters return immutable config that cannot change during a parse() call, yet they were invoked on every character (a few times per character in the hot states — isset(getSeparators()[$curChar]) etc.). Fetch them once into locals before the loop:

$separators = $this->options->getSeparators();
$bannedChars = $this->options->getBannedChars();
$useWhitespaceAsSeparator = $this->options->getUseWhitespaceAsSeparator();

This removes a method call and its surrounding opcodes from every character iteration — the gain is larger than the getters' own self-time because it also shrinks the enclosing parse() loop-body opcode count.

Result

~19% faster on a mixed-input micro-benchmark (87.8 → 71.0 μs/parse), on top of #60. The benchmark CI job on this PR measures head-vs-master per subject automatically.

Safety

• Immutable during a parse: no ParseOptions setter runs mid-parse(), so the hoisted values are loop-invariant.
• Behavior-preserving: all 91 tests pass, PHPStan level 8 / cs clean.

Context: diminishing returns

For transparency — the profile also confirmed the low-hanging fruit is now gone:

• mb_str_split is only ~0.3% of parse time; an ASCII str_split fast-path measured net-negative (the ASCII-detection check costs more than it saves).
• idn_to_ascii is ~0.7% (already ASCII-fast-pathed), NFC only runs in intl modes.

Remaining cost is spread across the state machine and per-address object construction. Further gains would need structural changes (e.g. reworking the result-object building) with more risk for less reward.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.89%. Comparing base (30b9e9a) to head (94dc39f).

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #61      +/-   ##
============================================
- Coverage     93.17%   92.89%   -0.29%     
  Complexity      380      380              
============================================
  Files             6        6              
  Lines           982      985       +3     
============================================
  Hits            915      915              
- Misses           67       70       +3     

Files with missing lines	Coverage Δ
src/Parse.php	90.11% <100.00%> (-0.40%)	⬇️

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