[duongynhi000005-oss]

Summary

Fixes #537

When SetInterspersed(false) is configured together with PassUnknownFlagToArgs, unknown flags are treated as non-flag arguments and placed into Args(). Previously:

• parseArgs appended the unknown flag to f.args and continued parsing, consuming later known flags instead of leaving them for the wrapped command.
• parseShortArg continued scanning remaining characters in a shorthand cluster after encountering an unknown shorthand (e.g. -uk), consuming trailing known shorthands.

Changes

• In parseShortArg, when !f.interspersed, append any remaining characters of the shorthand cluster to UnknownFlags and stop scanning the cluster.
• In parseArgs, when !f.interspersed, append all remaining args to f.args and return immediately after recording the unknown flag.
• Added TestPassUnknownFlagToArgsWithNonInterspersed covering long unknown flags (--unknown --known), standalone short unknown flags (-u -k), shorthand clusters (-uk --known and -ku --after), and ParseAll.

[Ekko82]

Verified 9a98e1e on Windows/amd64 with Go 1.27.1 against base f8a99067. I checked 17 cases through both Parse and ParseAll: all 34 checks pass on head, while 22 fail on base.

With SetInterspersed(false) and PassUnknownFlagToArgs, the additional cases confirm that an unknown argument protects the wrapped command's --help, invalid or missing integer values, and literal -- from further parsing. Attached shorthand values and the unprocessed cluster suffix are preserved. A known negative integer before the unknown argument still parses, and the interspersed-mode controls keep their previous behavior.

The added TestPassUnknownFlagToArgsWithNonInterspersed also passes unchanged. Validation covered these targeted probes and the added regression; the full suite, race detector, vet and lint were not run.