sh-syntax gaps covered by unbash #7

Compared with sh-syntax v0.6.0 (published Jul 8, 2026, bundling mvdan/sh v3.13.1), unbash handles valid Bash cases and avoids printer correctness bugs that remain open in the upstream tracker:

• Associative-array indexes containing # and array elements beginning with bracket globs (#1285, #558)
• Function names containing bracket suffixes, such as foo[foo]() (#1013)
• Preserving {array[index]} file-descriptor variable redirects without inserting a meaning-changing space (#719)
• Preserving the semantics of quoted legacy backtick substitutions when printing (#1083)
• Keeping a trailing backslash at EOF stable across repeated parse/print cycles (#1354)