fix(Types): Move distinct types into distinct identifiers

This allows types to be collected; prior to this commit they
   were conflicting from different modules.

   Uses this fix to extend sqrt to bigint, with the convention
   that it is undefined for non-perfect squares when 'predictable'
   is false and is the "best" approximation to the square root when
   'predictable' is true. Furthermore, for negative bigints, you might
   get a Gaussian integer when predictable is false; or you will just get
   your argument back when 'predictable' is true because what other
   bigint could you give back for a negative bigint?

   Also had to modify tests on the sign in sqrt(Complex) and add functions
   'zero' and 'one' to get types to match, as expected in #27.

   Adds numerous tests.

   Resolves #26.
   Resolves #27.

src/bigint/zero.mjs

@@ -0,0 +1,3 @@
+export * from './Types/bigint.mjs'
+
+export const zero = {bigint: () => () => 0n}