refactor: miniooni should be outside of the engine (#206)

* refactor: miniooni should be outside of the engine

This is part of https://github.com/ooni/probe/issues/1335. We also need
to think whether we wanna keep libminiooni and miniooni separated.

The previous use case for having a top-level libminiooni was that of
enabling others to integrate miniooni into other binaries.

This was usegul when studying internet censorship in Spain in May 2020.

I am wondering whether we should be keeping this complexity. I am not
sure about this and probably we should be killing it.

(In any case, reducing complexity is not the objective of this diff,
since I would like instead to move things around with minimal changes
and make sure we have a ~good repository organization here.)

* fix: import in libminiooni

internal/engine/humanizex/humanizex.go

@@ -0,0 +1,26 @@
+// Package humanizex is like dustin/go-humanize
+package humanizex
+
+import "fmt"
+
+// SI is like dustin/go-humanize.SI
+func SI(value float64, unit string) string {
+	value, prefix := reduce(value)
+	return fmt.Sprintf("%3.0f %s%s", value, prefix, unit)
+}
+
+func reduce(value float64) (float64, string) {
+	if value < 1e03 {
+		return value, " "
+	}
+	value /= 1e03
+	if value < 1e03 {
+		return value, "k"
+	}
+	value /= 1e03
+	if value < 1e03 {
+		return value, "M"
+	}
+	value /= 1e03
+	return value, "G"
+}

internal/engine/humanizex/humanizex_test.go

@@ -0,0 +1,34 @@
+package humanizex_test
+
+import (
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/humanizex"
+)
+
+func TestGood(t *testing.T) {
+	if humanizex.SI(128, "bit/s") != "128  bit/s" {
+		t.Fatal("unexpected result")
+	}
+	if humanizex.SI(1280, "bit/s") != "  1 kbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if humanizex.SI(12800, "bit/s") != " 13 kbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if humanizex.SI(128000, "bit/s") != "128 kbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if humanizex.SI(1280000, "bit/s") != "  1 Mbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if humanizex.SI(12800000, "bit/s") != " 13 Mbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if humanizex.SI(128000000, "bit/s") != "128 Mbit/s" {
+		t.Fatal("unexpected result")
+	}
+	if humanizex.SI(1280000000, "bit/s") != "  1 Gbit/s" {
+		t.Fatal("unexpected result")
+	}
+}