fix: return complete pattern parts from scan

[mrmlnc]

Fixes #58. This PR depends on #197, because makes this fix simpler by enabling full-pattern scanning for tokens.

Summary

scan() did not always return a complete representation of pattern segments when parts was enabled.

This change:

• preserves leading and trailing empty segments;
• returns a single part for patterns without path separators;
• excludes prefixes such as ! and ./ from returned parts;
• keeps slashes inside balanced parentheses in the same part;
• handles nested and escaped parentheses;
• splits only on top-level, unescaped path separators.

Examples

scan('/', { parts: true }).parts
// ['', '']

scan('/a/b', { parts: true }).parts
// ['', 'a', 'b']

scan('(!(b/a))', { parts: true }).parts
// ['(!(b/a))']

scan('./directory/(a|b)/*.js', { parts: true }).parts
// ['directory', '(a|b)', '*.js']

[github-code-quality]

Code Coverage Overview

Languages: JavaScript

JavaScript / code-coverage/nyc

The overall line coverage in commit f201165 in the issue-58 branch is 96%. Line coverage data for the master branch is not yet available.

Show a line coverage summary of the most covered files.

File	master	issue-58 f201165	+/-
lib/constants.js	—	100%	—
index.js	—	100%	—
posix.js	—	100%	—
lib/scan.js	—	99%	—
lib/parse.js	—	95%	—
lib/picomatch.js	—	95%	—
lib/utils.js	—	90%	—