std.abs(0) incorrectly returns -0 (negative zero)

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Bug Description

std.abs(0) returns -0 instead of 0. The absolute value of zero should always be positive zero.

Reproduction

std.abs(0)

Expected Behavior

0

Actual Behavior

-0

Notably, std.abs(-0) correctly returns 0:

std.abs(-0)  // returns 0 (correct)
std.abs(0)   // returns -0 (incorrect)

Version

$ jsonnet --version
Jsonnet commandline interpreter (Go implementation) v0.22.0

Analysis

This is likely caused by the implementation using math.Copysign or similar, which copies the sign bit incorrectly. The Go math.Abs function should handle this correctly:

// math.Abs(0) in Go returns 0 (positive zero)
// math.Abs(-0) in Go returns 0 (positive zero)

sjsonnet correctly returns 0 for both std.abs(0) and std.abs(-0).