Explicitly qualify Base.Bool constructor

[rossviljoen]

Fixes a precompilation warning in julia 1.12:

┌ FixedPointDecimals
│  WARNING: Constructor for type "Bool" was extended in `FixedPointDecimals` without explicit qualification or import.
│    NOTE: Assumed "Bool" refers to `Base.Bool`. 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 Bool end`.
│    Hint: To silence the warning, qualify `Bool` as `Base.Bool` in the method signature or explicitly `import Base: Bool`.
└  

[rossviljoen]

fixes #119