Add isApproximatelyEqual for RandomAccessCollection

I think it would be useful to add `isApproximatelyEqual` for `RandomAccessCollection`. When working with numerical computations on collections of floating-point values (e.g., vectors, matrices represented as arrays), it's common in tests to need element-wise approximate equality comparisons. The API would mirror the existing scalar versions:

```swift
extension RandomAccessCollection where Element: Numeric, Element.Magnitude: FloatingPoint {
@inlinable @inline(__always)
public func isApproximatelyEqual(
to other: Self,
relativeTolerance: Element.Magnitude = Element.Magnitude.ulpOfOne.squareRoot(),
norm: (Element) -> Element.Magnitude = \.magnitude
) -> Bool {
return isApproximatelyEqual(
to: other,
absoluteTolerance: relativeTolerance * Element.Magnitude.leastNormalMagnitude,
relativeTolerance: relativeTolerance,
norm: norm
)
}

@inlinable @inline(__always)
public func isApproximatelyEqual(
to other: Self,
absoluteTolerance: Element.Magnitude,
relativeTolerance: Element.Magnitude = 0
) -> Bool {
return isApproximatelyEqual(
to: other,
absoluteTolerance: absoluteTolerance,
relativeTolerance: relativeTolerance,
norm: \.magnitude
)
}
}

extension RandomAccessCollection where Element: AdditiveArithmetic {
@inlinable
public func isApproximatelyEqual(
to other: Self,
absoluteTolerance: Magnitude,
relativeTolerance: Magnitude = 0,
norm: (Element) -> Magnitude
) -> Bool
where Magnitude: FloatingPoint {
guard self.count == other.count else { return false }
for (lhs, rhs) in zip(self, other) {
if !lhs.isApproximatelyEqual(
to: rhs,
absoluteTolerance: absoluteTolerance,
relativeTolerance: relativeTolerance,
norm: norm
) {
return false
}
}
return true
}
}

```

I'm happy to submit a PR with tests if this sounds reasonable.

The issue provides the proposed RandomAccessCollection API and asks for tests. Start by locating the existing scalar isApproximatelyEqual entry points, then add collection coverage for equal counts and element-wise comparisons. Done means the overloads are implemented and the proposed tests pass.

Written by the indexing model from the issue text.