Fixed-width bitwise inverse of `isZero`

[oscbyspro]

As mentioned in (#103), I've found some value in the bitwise inverse isZero.

extension ANKFixedWidthInteger {

    /// Returns whether all its bits are set, in two's complement form.
    ///
    /// The returned value can be viewed as the bitwise inverse of ``isZero``.
    ///
    /// ```swift
    ///  Int8(0b_1111_1111).isFull // true
    /// UInt8(0b_1111_1111).isFull // true
    ///  Int8(0b_1111_1110).isFull // false
    /// UInt8(0b_1111_1110).isFull // false
    /// ```
    ///
    @_transparent public var isFull: Bool {
        nonzeroBitCount == bitWidth 
        // OR self == ~(0 as Self)
        // OR low.isFull && high.isFull
    }
}

[oscbyspro]

Hm. I believe I want this—not necessarily because isFull is the most useful thing ever made, but because I need an efficient, non-allocating, way of matching a repeating bit. I've played with the following, and I find it easy to reason about. I mean, I already have init(repeating:) because it comes up a lot:

@_transparent public func matches(repeating bit: Bool) -> Bool {
    bit ? isFull : isZero
}

[oscbyspro]

I admit that isFull sounds like is collection property, relating in some way to isEmpty. Having said that, it makes sense considering an isFull integer cannot be modified by the OR operator.