feat: add assertArrayEmpty

[hughgrigg]

Adds assertArrayEmpty and the emptyArray() matcher, the positive counterpart to assertArrayNotEmpty and nonEmptyArray(). Before this, assertArrayNotEmpty was the only negated assertion in the set whose twin was missing.

Resolves #117

What changes

assertArrayEmpty(value, message?) narrows to [], or to readonly [] where the calling scope already knows the array is readonly. emptyArray() does the same through assertObjectMatches. Both follow the pair in src/assert/array-not-empty/.

The failure message names the elements that are present, which is usually the diagnostic the assertion exists to produce.

Expected array ["DenyRegions: unsupported condition key aws:RequestedRegion"] (len 1) to be empty.

A non-array value mirrors the branch assertArrayNotEmpty already has (Expected string "abc" to be an empty array.).

The lint selector

prefer-specific-assertions now steers assertArrayLength(value, 0) at the new assertion. This is the first selector in the table that starts from a specific assertion rather than from assertIdentical, assertTrue or assertFalse.

That is safe here for a reason worth recording. The file comment explains that neither linter has type information, which is what keeps assertTrue(value.length === 0) and assertFalse(value.length === 0) out of the table (a selector cannot tell a string receiver from an array one, and the array assertions throw on strings). assertArrayLength has already committed to an array in its callee name, so that ambiguity does not arise. A literal 0 in the length position is the only shape that matches, leaving assertArrayLength(values, 2), assertArrayLength(values, expected) and assertStringLength(text, 0) alone.

Notes

assertArrayLength(value, 0) already narrowed correctly, since ArrayOfLength<T, 0> resolves to []. The gap this closes is in how the call reads and how it fails, not in the type.

src/index.ts and the README lists are generated, so both are regenerated output rather than hand edits.

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