Blink parity: glue by-reference arrow fn space; gate to 0.1%

[TomasVotruba]

Removes the space in a by-reference arrow function. Measured drop: 5 to 4 differing files of 4527 (0.088%).

The fix

FunctionDeclarationFixer with closure_fn_spacing=none (the mautic config) clears the whitespace right after the fn keyword for a lambda, regardless of a following &. blink only did so when ( directly followed fn, so fn &() kept its space:

return \Closure::bind(fn&() => $this->{$property}, $this, parent::class)();

fnIsArrowFn now also recognizes the by-reference form fn &(, so the space is glued.

Gate

MAX_DIFF_PERCENT lowered 0.15 to 0.1; actual is 0.088% (4 of 4527).

Unit tests cover by-ref glue under none and the single-space kept under one. Full blink suite, go vet, golangci-lint green; strict rector-src 1:1 gate stays 0-diff.

Remaining 4 (blocked - require ECS-quirk or lexer changes)

• FieldsTypeTrait: list-destructuring expansion is a context-dependent position-staleness artifact (expands only when nested in a closure-as-array-value; top-level stays single-line), so a general rule would over-apply and break the rector gate.
• webhook-failing / webhook-killed.html.php: ECS's ArrayIndentation emits an internally-inconsistent 4/12/0 indent for an array opener buried mid-line in a T_INLINE_HTML token; matching it means emulating a php-cs-fixer quirk not provably safe for the rector gate.
• SummarizeCommand: array inside a complex-interpolation string; reflowing needs the lexer to tokenize {$...} contents, which blink treats as atomic - a change that ripples across every interpolated string and cannot keep the 1705-file rector gate at 0-diff.