Using Fibers causes epic crash

[withinboredom]

Minimal code to reproduce:

<?php

do {
 $running = false;
 //$running = frankenphp_handle_request(function (): void {
 $fiber = new Fiber(function() {
 echo "Starting Fiber\n";
 });
 $fiber->start();
 //});
} while ($running);

With some slight modifications, it can also be reproduced in worker mode.

[withinboredom]

@dunglas the following Docker file (props @cdaguerre in #374) appears to "fix" fibers. At least for this reproducer with manual testing. It needs more testing:

FROM dunglas/frankenphp:latest-builder-php8.3-alpine AS builder

COPY --from=caddy:builder-alpine /usr/bin/xcaddy /usr/bin/xcaddy

ENV CGO_ENABLED=1 XCADDY_SETCAP=1 CGO_CXXFLAGS=-fPIE CGO_CFLAGS=-fPIE CGO_LDFLAGS=-pie XCADDY_GO_BUILD_FLAGS='-buildmode=pie -ldflags="-w -s" -trimpath'
RUN xcaddy build \
 --output /usr/local/bin/frankenphp \
 --with github.com/dunglas/frankenphp=./ \
 --with github.com/dunglas/frankenphp/caddy=./caddy/ \
 --with github.com/dunglas/mercure/caddy \
 --with github.com/dunglas/vulcain/caddy

🥳 🤞 🤞 still testing...

[dunglas]

Great news! Don't hesitate to open a PR with this changes, so we can see if this fix the issue for all architectures.

[withinboredom]

I'll do some proper testing by Monday (by updating the fiber branch), but I haven't seen a crash yet via manual testing.