feat: Template types for Pocomath

Tuple<T> and a couple of functions on it are now working according to
  the target spec. As desired, no instantiations of a template type
  are made until some function that takes an instantiation is called.

test/tuple/_native.mjs

@@ -3,7 +3,26 @@ import math from '../../src/pocomath.mjs'
 
 describe('tuple', () => {
    it('can be created and provide its length', () => {
-      assert.strictEqual(math.length(math.tuple(3,5.2,2n)), 3)
+      assert.strictEqual(math.length(math.tuple(3, 5.2, 2)), 3)
+   })
+
+   it('does not allow unification by converting consecutive arguments', () => {
+      assert.throws(() => math.tuple(3, 5.2, 2n), /TypeError.*unif/)
+      // Hence, the order matters in a slightly unfortunate way,
+      // but I think being a little ragged in these edge cases is OK:
+      assert.throws(
+         () => math.tuple(3, 2n, math.complex(5.2)),
+         /TypeError.*unif/)
+      assert.deepStrictEqual(
+         math.tuple(3, math.complex(2n), 5.2),
+         {elts: [math.complex(3), math.complex(2n), math.complex(5.2)]})
+   })
+
+   it('can be tested for zero', () => {
+      assert.strictEqual(math.isZero(math.tuple(0,1)), false)
+      assert.strictEqual(math.isZero(math.tuple(0n,0n,0n,0n)), true)
+      assert.strictEqual(math.isZero(math.tuple(0,0.001,0)), false)
+      assert.strictEqual(math.isZero(math.tuple(0,math.complex(0,0))), true)
    })
 
 })