fix(set): support bundled -o in short-flag clusters (set -euo pipefail) (#261)

* fix(set): support bundled -o in short-flag clusters (set -euo pipefail)

`set -euo pipefail` previously failed with `bash: set: -o: invalid
option`: the cluster parser treated every character after `-` as an
independent short flag and has no `o` flag, so `-o` was only honored as
its own token.

Match bash: an `o` inside a cluster consumes the next word as its
long-option name, and the remaining characters keep being parsed as
short flags. `set -euo pipefail` == `set -e -u -o pipefail`,
`set -oe pipefail` enables both pipefail and errexit, trailing words
become positional parameters, `+`-clusters disable, and an invalid
bundled name still reports `invalid option name`.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(set): apply remaining cluster flags after a no-name bundled -o

A bundled `o` with no following option-name word (e.g. `set -oe`) was
returning early after printing the option listing, abandoning the rest of
the short-flag cluster. Real bash still applies every flag — `set -oe`
enables errexit and prints the listing — so defer the listing and keep
processing the remaining flags, flushing the accumulated listing at the end.

Addresses Vercel Agent Review feedback on the bundled-`-o` change.

Co-authored-by: Cursor <cursoragent@cursor.com>

* test(set): cover multiple bundled -o consuming successive words

Adds a regression test for `set -oo pipefail errexit`, addressing Copilot's
suggestion to cover the multi-`o` edge case alongside the no-name listing
fallback tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(set): keep processing tokens after a no-name -o/+o listing

A standalone `-o`/`+o` with no option-name word (e.g. `set -o -x`) returned
early after printing the listing, dropping any following tokens. bash prints
the listing and continues — `set -o -x` lists options and then enables
xtrace — so defer the standalone listing the same way as the bundled case and
flush it at the end. Clarifies that an option-like token (`-x`) is not
consumed as the `-o` name, and adds a `set -o -x` regression test.

Co-authored-by: Cursor <cursoragent@cursor.com>

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Co-authored-by: Cursor <cursoragent@cursor.com>