fix brace alternation scanning with character classes

[sidsri14]

Summary

Fixes #113. A character class inside a brace alternation (e.g. {[}],a} or {[a,b]x.md,real/path.txt}) was not skipped when the matcher scanned for the next alternative or the matching closing brace, so commas and braces contained in the class were treated as alternation syntax. As a result, ValidatePattern blessed patterns that Match could never match.

Root cause

Two helper scanners didn't account for character classes:

• indexNextAlt (utils.go) — found the comma splitting alternatives; a comma inside a class was misread as a separator.
• indexMatchedClosingAlt (match.go) — found the matching }; a } inside a class was misread as the closing brace.

The validator (doValidatePattern) already skips character classes correctly, which is why it approved these patterns while the matcher rejected them.

Change

Skip [...] character classes (including escaped bytes inside them) in both scanners, mirroring what the validator already does. This applies only when the pattern uses / as the separator; on systems where \ is the separator, escaping is disabled and classes are skipped at face value.

Tests

Added regression rows to matchTests covering both a comma and a closing-brace inside a character class within a brace alternation:

• {[a,b]x.md,real/path.txt} matches ax.md, bx.md, real/path.txt, but not cx.md
• {[}],a} matches }, a, but not b

Verified the rows fail on unpatched upstream (TestMatch reported "syntax error in pattern" for these patterns) and pass with this change. Full suite: go test -count=1 ./... → ok, go vet clean.

Notes

• No behavior change for patterns without character classes inside alternations.
• No CHANGELOG file exists in this repo; commit follows existing short-imperative style.

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Assistance disclosure: this change was developed with the help of an AI coding assistant (Claude Code by Anthropic).

[bmatcuk]

Looks like a good fix to me... I made some changes to your tests so that they'll actually run on-disk (ie, exercise Glob).