fix(gnovm): allow multiple NaN keys in maps

[mvertes]

The behavior of maps with NaN now matches Go.

Fixes #3867.

[Gno2D2]

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[codecov]

Codecov Report

Attention: Patch coverage is 69.23077% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
gnovm/pkg/gnolang/values.go	69.23%	6 Missing and 2 partials ⚠️

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[thehowl]

1. this is currently only working for float64, not float32 :)
2. alas, it looks like we currently do a bad job of just comparing floats. maybe we should look at improving how floats are canonicalized more generally?

// You can edit this code!
// Click here and start typing.
package main

import "fmt"

func main() {
	a := 0.0
	b := map[float64]int{a: 1, a * -1: 2}
	println(b)
	println(a == (a * -1))
}

this makes a one-element map in go, but a two-element map in gno.

[mvertes]

The key identity was defeated by the fact that +0.0 is encoded differently from -0.0, due to the presence of a sign bit in the IEEE 754 format. I fixed this by alway clearing the sign bit if value equals to 0.

Remaining special values +Inf and -Inf do not require special processing for maps, so we should be good now for using floats as map keys.

The above sample for +0.0 vs -0.0, once fix applied, raises another separate issue that we have in general with literal composite expressions: #3964. I will provide a test with floating point keys in the PR fixing it.