perf: Always return arrays from parsePropertyValue

[domenic]

The inArray parameter caused cache thrashing: CSSStyleDeclaration.js
called without it (caching strings) while property files called with
inArray: true (expecting arrays). When the cached type didn't match
what a caller needed, it would recompute and overwrite, causing the
next different-type caller to also miss. By always returning arrays,
all callers can share the same cached results.

🤖 Generated with Claude Code

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To-do before merging:

• Human code review (@asamuzaK welcome to help)
• Double-check benchmark improvements manually
• Double-check the full jsdom test suite passes

[asamuzaK]

We can remove all { globalObject }, not just this file.
See #280 (comment)

[domenic]

Yeah, I was thinking of including that in this PR but it's simpler to just focus this PR on isArray.

[asamuzaK]

LGTM

[domenic]

Without changes

# style/createElement + setAttribute('style') #
jsdom  x 193 ops/sec ±2.69% (77 runs sampled)

# style/createElement + style properties #
jsdom  x 234 ops/sec ±2.11% (81 runs sampled)

# style/createElement + style.cssText #
jsdom  x 202 ops/sec ±2.49% (80 runs sampled)

# style/innerHTML: divs with inline styles #
jsdom  x 181 ops/sec ±2.50% (79 runs sampled)

# style/innerHTML: simple divs (no styles) #
jsdom  x 5,059 ops/sec ±2.38% (84 runs sampled)

With changes

# style/createElement + setAttribute('style') #
jsdom  x 193 ops/sec ±2.80% (77 runs sampled)

# style/createElement + style properties #
jsdom  x 246 ops/sec ±2.45% (79 runs sampled)

# style/createElement + style.cssText #
jsdom  x 205 ops/sec ±2.93% (78 runs sampled)

# style/innerHTML: divs with inline styles #
jsdom  x 205 ops/sec ±2.32% (79 runs sampled)

# style/innerHTML: simple divs (no styles) #
jsdom  x 4,727 ops/sec ±2.03% (85 runs sampled)

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Not a huge improvement but since it makes the code simpler anyway, let's merge.