Better handling of malformed messages

[jwoertink]

Fixes #67

This PR refactors how the Payload is created in order to better handle when a message comes through with malformed data. It also gives us a bit of a performance boost by moving the Payload over to structs!

❯ ./bench 
new_payload 677.95  (  1.48ms) (± 5.55%)  2.92MB/op        fastest
old_payload 513.67  (  1.95ms) (± 5.67%)  4.37MB/op   1.32× slower

Explanation

The current Payload makes a lot of assumptions about the shape of the JSON being parsed. It first assumes valid JSON is passed in, then assumes that the valid JSON is an Object. The handler generally just does a blanket JSON::ParsingError catch on this.

Now if we get an empty string, we can just ignore it, and if the JSON structure is valid, it'll be a full serialized object we can pass around easier. If the Payload can't be deserialized, then we raise the serialized error and let the handler do as it does.

[jwoertink]

This is because Ameba tanks on 1.6.0 under alpine

ref: crystal-ameba/ameba#354

[fernandes]

nice! so do not consider what I commented on the issue lol

[fernandes]

ohhh now I see what you're saying about the payload on the connection, maybe I misunderstood the issue 🤦

this is cool for sure, even better with the performance boost 👏