Previously, a character class containing any builtin (\d, \w, \s)
forced the compiler down the slow "complex class" path, which emits
a disjunction of alternatives and backtracks at runtime.
For non-unicode, non-unicode-sets, non-negated classes, \w and \d
can be inlined as their raw ASCII code-point ranges. The resulting
class stays on the fast path and compiles into a single sorted
CharClass instruction.
The unicode/unicode_sets and negation guards are required for
correctness: with the /u + /i flags, \w gains non-ASCII members
via case folding (e.g. U+017F, U+212A), and negated classes have
a separate, smarter compilation path.
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