feat: add support for disabling signature verification

[zBNF]

During local development it doesn't make a lot of sense to require signature verification.

Here's a proposed change that allows library users to disable verification. I'm open to alternative approaches in order to avoid introducing any breaking changes if there are concerns around that.

[diamondburned]

Discord won't allow using a new endpoint without having the valid signature in the first place.

I'm not sure what you're actually trying to accomplish by having this PR. I personally develop my bot just fine with this. Are you trying to mock test the bot? Why not just call the handler function directly?

[diamondburned]

A non-breaking way to introduce this would be to not do verification if pubkey == "". This way, you can empty out the environment variable for the pubkey within development. No new parameters need to be introduced.

[zBNF]

I think this works.

Are you trying to mock test the bot?

Basically, I'm looking to run black box tests using mocks on my binary.