In theory this can optimize some code paths where a string first needs
to be converted to a []byte to use the normal Write method. By
implementing WriteString this extra copy isn't needed. Internall we
don't do the copy and just use s2b instead.
- I noticed that fasthttp was taking up 1.8MB of heap memory, even
though it wasn't being used. This turned out to be the stackless
function: 1.80MB github.com/valyala/fasthttp/stackless.NewFunc
- Lazy load the stackless functions with sync.Once, given this a simple
atomic read, it shouldn't affect performance for the fast-path (I
haven't seen benchmarks with compression enabled).