perf(unionfind): optimize UnifyTermsExtend map duplication

[apocalypse9949]

Added a Copy() method to UnionFind that pre-allocates the map capacity using the length of the parent map (len(uf.parent)). This prevents unnecessary memory reallocations and rehashing when duplicating the union-find structure.

UnifyTermsExtend was refactored to use this Copy() method instead of creating an empty map and copying elements manually, resulting in a significant performance improvement for repetitive inference loops.

Before this change, copying unionfind base would iteratively populate an empty map:

// UnifyTermsExtend unifies two same-length lists of relational terms, returning
// an extended UnionFind. It does not handle apply-expressions.
func UnifyTermsExtend(xs []ast.BaseTerm, ys []ast.BaseTerm, base UnionFind) (UnionFind, error) {
	if len(xs) != len(ys) {
		return UnionFind{}, fmt.Errorf("not of equal size")
	}
	uf := UnionFind{make(map[ast.BaseTerm]ast.BaseTerm)}
	for k, v := range base.parent {
		uf.parent[k] = v
	}
// ...

After the change, memory pre-allocation avoids multiple resize pauses:

// Copy returns a new UnionFind that is a copy of this one.
func (uf UnionFind) Copy() UnionFind {
	newUf := UnionFind{make(map[ast.BaseTerm]ast.BaseTerm, len(uf.parent))}
	for k, v := range uf.parent {
		newUf.parent[k] = v
	}
	return newUf
}

// UnifyTermsExtend unifies two same-length lists of relational terms, returning
// an extended UnionFind. It does not handle apply-expressions.
func UnifyTermsExtend(xs []ast.BaseTerm, ys []ast.BaseTerm, base UnionFind) (UnionFind, error) {
	if len(xs) != len(ys) {
		return UnionFind{}, fmt.Errorf("not of equal size")
	}
	uf := base.Copy()
// ...

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[burakemir]

Added in 69dc00f - thanks for your contribution!