fix(core): enforce the array length limit when the inner schema has a default

[173787247]

What happens

The lower bound is not checked at all when inner carries a default:

Schema.array(Schema.string()).min(2)([])                 // throws: expected array length >= 2 but got 0
Schema.array(Schema.string().default('x')).min(2)([])    // returns []   ← the bound is skipped

max is unaffected, so only min is dropped. It is also not limited to scalar inners —
Schema.array(Schema.object({ a: Schema.string().default('y') })).min(2)([]) passes too.

packages/core/src/index.ts:654:

checkWithinRange(data.length, meta, 'array length', options, !isNullable(inner!.meta.default))
//                                                          ^ skipMin

Where the guard came from

0de846e3 (feat: enhance length check for array) added two things in the same hunk,
and also touched form/src/extensions/group.vue, table.vue and utils.ts:

+ while (data.length && isNullable(data[data.length - 1])) data.pop()
  checkWithinRange(data.length, meta, 'array length', !isNullable(inner!.meta.default))

The form pads short arrays with blank rows (packages/form/src/utils.ts:119-122, result.push(['' + result.length, null])),
so the pop() dropped those rows and skipMin kept the now-shorter array from failing the bound.
The pair was self-consistent.

f61fafda (fix: fix indexing for group entries, fix koishijs/koishi#1381) removed the pop()
on its own — +0/-1, one line, unrelated commit message — and left skipMin behind:

- while (data.length && isNullable(data[data.length - 1])) data.pop()
  checkWithinRange(data.length, meta, 'array length', !isNullable(inner!.meta.default))

Removing it looks right: it mutated the caller's array. But the guard it was paired with
has been skipping the bound for every defaulted inner schema since then, not only for padded input.

The form still pads to min before the value is validated, so it does not depend on the guard.

Test

Added to the existing array (length) test in packages/core/tests/array.spec.ts
rather than a new file:

test('array (length) with a defaulted inner', () => {
  const Config = Schema.array(Schema.string().default('x')).min(2)

  expect(() => new Config([])).to.throw()
  expect(() => new Config(['dress'])).to.throw()

  expect(new Config(['dress', 'skirt'])).to.deep.equal(['dress', 'skirt'])
  expect(new Config(['dress', null])).to.deep.equal(['dress', 'x'])
})

yarn yakumo test core, with the test present and the source change reverted:

ℹ tests 48    ℹ pass 45    ℹ fail 2
✖ array (length) with a defaulted inner
  Error [AssertionError]: expected [Function] to throw an error

and with the change applied:

ℹ tests 48    ℹ pass 46    ℹ fail 1
✔ array (length) with a defaulted inner (1.01ms)

The one remaining failure is I18n > basic support (i18n.spec.ts:46), which fails on
unmodified main as well:

# baseline, no changes
ℹ tests 47    ℹ pass 45    ℹ fail 1    ℹ skipped 1