test: add regression for non-count option with value 1

[ZhouYinLong-lab]

What changed

Added a regression test for non-count options that receive a value of 1.

Why

When passing -x 3 -x 1, the parser incorrectly treats the 1 as a count increment, returning x: 4 instead of x: [3, 1]. The root cause is in setKey() where value === increment() (which is 1) gates the increment logic, incorrectly matching actual values of 1.

Verification

parser("-x 3 -x 1")
// Expected: x: [3, 1]
// Actual:   x: 4  ← bug: 3 + 1 = 4

The test currently fails as expected.

Related issue

Refs #506

[shadowspawn]

1. This looks like AI slop
2. These is already an open PR fix(setKey): use a sentinel to detect count auto-increment #529