Fix warning on Julia 1.12

[devmotion]

When loading ComplexityMeasures on Julia 1.12, the following warning is shown:

julia> using ComplexityMeasures
...
┌ ComplexityMeasures
│  WARNING: Constructor for type "Integer" was extended in `ComplexityMeasures` without explicit qualification or import.
│    NOTE: Assumed "Integer" refers to `Base.Integer`. This behavior is deprecated and may differ in future versions.`
│    NOTE: This behavior may have differed in Julia versions prior to 1.12.
│    Hint: If you intended to create a new generic function of the same name, use `function Integer end`.
│    Hint: To silence the warning, qualify `Integer` as `Base.Integer` in the method signature or explicitly `import Base: Integer`.

The PR fixes this issue by qualifying Integer as Base.Integer, as suggested in the warning.