Deprecations after upgrading to PHP 8.4

[wesolydexter]

PHP 8.4: Implicitly nullable parameter declarations deprecated.

Zipkin\RealSpan::start(): Implicitly marking parameter $timestamp as nullable is deprecated, the explicit nullable type must be used instead in vendor/openzipkin/zipkin/src/Zipkin/RealSpan.php line 55

Deprecated: Zipkin\Tracer::nextSpanWithSampler(): Implicitly marking parameter $contextOrFlags as nullable is deprecated, the explicit nullable type must be used instead in /srv/api/vendor/openzipkin/zipkin/src/Zipkin/Tracer.php on line 230

Deprecated: Zipkin\Tracer::nextSpan(): Implicitly marking parameter $contextOrFlags as nullable is deprecated, the explicit nullable type must be used instead in /srv/api/vendor/openzipkin/zipkin/src/Zipkin/Tracer.php on line 196

and more...

https://php.watch/versions/8.4/implicitly-marking-parameter-type-nullable-deprecated

It would be great to fix this 😅

[wesolydexter]

#231

[wesolydexter]

Done.