fix: read fore/background colors on first access

Caching the colors in OutputOption makes the order of options important.
For example, if you're using WithUnsafe _after_ WithColorCache, the
colors wouldn't respect the `unsafe` option since the colors get cached
_during_ the execution of WithColorCache option.

Another example, is the use of a custom environ using the WithEnvironment
option. If WithEnvironment comes _before_ WithColorCache, reading the
terminal colors won't respect the values in the environment.

Instead, don't read the colors in WithColorCache and make the user
opt-in if they want to cache the colors right after creating a new
output using ForegroundColor and BackgroundColor.

```go
// To cache the colors after creating an output
output := NewOutput(os.Stderr)
_ = output.ForegroundColor()
_ = output.BackgroundColor()
```

output.go

@@ -104,14 +104,10 @@ func WithProfile(profile Profile) OutputOption {
 }
 
 // WithColorCache returns a new OutputOption with fore- and background color values
-// pre-fetched and cached.
+// cached on first access.
 func WithColorCache(v bool) OutputOption {
 	return func(o *Output) {
 		o.cache = v
-
-		// cache the values now
-		_ = o.ForegroundColor()
-		_ = o.BackgroundColor()
 	}
 }