chore: add benchmark showing a 2.5 reduction in memory usage since RC2

[dunglas]

This benchmark shows that #292 and #293 improve memory usage by a factor of 2.5!
The more data read from the request body or written in the response body, the more significant the improvement!

There is still room for similar improvements in:

frankenphp/frankenphp.go

Line 509 in 981f954

func go_register_variables(rh C.uintptr_t, trackVarsArray *C.zval) {

It would be nice if the memory wasn't allocated once in Go and a second time in C (and then a third time because of how PHP works internally). A possible way to improve this could be to populate the CGI variables directly in C-compatible strings, to avoid copyinv.

Before #292 and #293.

Memory usage: 14.9 bytes per request.

Running tool: /opt/homebrew/bin/go test -benchmem -run=^$ -bench ^BenchmarkEcho$ github.com/dunglas/frankenphp -v -count=1

goos: darwin
goarch: arm64
pkg: github.com/dunglas/frankenphp
BenchmarkEcho
BenchmarkEcho-8 3514 342450 ns/op 15261 B/op 32 allocs/op
PASS
ok github.com/dunglas/frankenphp 2.122s

After

5.3 bytes per request.

Running tool: /opt/homebrew/bin/go test -benchmem -run=^$ -bench ^BenchmarkEcho$ github.com/dunglas/frankenphp -v -count=1

goos: darwin
goarch: arm64
pkg: github.com/dunglas/frankenphp
BenchmarkEcho
BenchmarkEcho-8 3565 335976 ns/op 5482 B/op 28 allocs/op
PASS
ok github.com/dunglas/frankenphp 2.150s

[withinboredom]

A possible way to improve this could be to populate the CGI variables directly in C-compatible strings

If you add a "\0" onto the end of the go strings (strings in Go are not null terminated), and know the strings won't be mutated ... you could probably try this super hacky (untested) method to get the raw pointer from Go:

char* cstring = (*reflect.StringHeader)(unsafe.Pointer(&gostring)).Data

Maybe?