fix(core): Support multiple handlers for same paths

[offirgolan]

server.get('/ping').on('response', handler1);
server.get('/ping').on('request', handler2);

await fetch('/ping');

Given the above code sample, the expected behavior is that handler1 and handler2 would both be executed within the lifecycle of the request. The actual result was that only handler2 was getting executed because the router was overwriting the handler since the routes were the same.