Add more numeric predictates to cptypes

[gus-massa]

In particular, even?, odd?, positive?, negative?, real-valued? and similar primitives.

The support is only partial. It's enough to specialize

(lambda (x) (when (fixnum? x) (positive? x)))
==>
(lambda (x) (when (fixnum? x) (fxpositive? x)))

but it's not enough to reduce

(lambda (x) (when (positive? x) (positive? x)))
==>
(lambda (x) (when (positive? x) #t))

that require a big refinement in the internal type system (planed for later, let's say mid 2026).

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In primdata.ss/primvars.s I renamed nzuint to pint because all the other types use that convention.

I also made a few new types, to complement the old types:

• fixnum: all fixnums (some other types use an s, like sint, so perhaps it shoud be sfixnum)
• pfixnum: positive, i.e. >0
• nfixnum: (new) negative, i.e. <0
• ufixnum: unsigned/"up", i.e. >=0
• dfixnum: (new) ???/"down", i.e. <=0

I didn't find a nice name/letter for "<=0", but since u is used for unsigned ">=0", we can reinterpret is as up/down. The letter d is visually different from the others letters to be easy to notice, and it a nice mnemonic.