fix: apply prepend as a string on generated regexes (#110)

[cpruijsen]

Summary

• Document options.prepend as a string (it was listed as boolean while the description, micromatch, and the parser all treated it as a string).
• Copy that string into the generated regex for ordinary patterns, not only after the parser backtracks.
• Skip tokenizer fast paths when prepend is set, because those paths never see the beginning-of-string token that holds it.
• When the tokenizer recursively parses a suffix after a negated extglob (for example !(*.d).ts), do not pass prepend back into parse(), or the prefix is applied twice and excluded names start matching.

Provenance: issue #110 reported the type/description mismatch. micromatch already documents this option as string. This repo already stored it as opts.prepend || '' on the beginning-of-string token.

Decision

• Chose: document it as string and honor that string on parse/makeRe output, including fast-path globs, by sending those globs through the tokenizer.
• Alternative: change only the type column and leave prepend as a no-op except on backtracking patterns (POSIX classes, some brace ranges). A second alternative is to concatenate the string inside parse.fastpaths / wrapOutput so fast-path regexes stay byte-identical aside from the prefix.
• Reasoning: the option was already a string on the bos token; the missing copy into state.output is what made the description false for most globs. Skipping fast paths keeps a single source of truth instead of assembling the prefix in three return sites. The cost is that prepended *.js / .* use full-parser semantics (the same as fastpaths: false), including no optional trailing slash on *.js.
• Offer: I can drop the parser change and keep the docs-only type fix if you prefer. I can also thread the string through the fast paths instead of skipping them if you want those regexes unchanged aside from the prefix.

Test plan

• npx mocha test/options.prepend.js, prepend appears on parse output, makeRe, fast-path globs like *.js, POSIX classes without doubling, and !(*.d).ts without doubling
• parse('abc', { prepend: 'foo' }).output === 'fooabc'
• makeRe('abc', { prepend: 'foo' }).source === '^(?:fooabc)$'
• isMatch('foofile.d.ts', '!(*.d).ts', { prepend: 'foo' }) === false
• Existing tests still pass (npx mocha)