Handle both number and string for rpc request method

[Odonno]

Thank you for submitting this pull request! We really appreciate you spending the time to work on these changes.

What is the motivation?

When consuming the /rpc endpoint, we have to pass the method name as a string. There is a small optimization to be done by only sending a small number.

What does this change do?

Handle both string and u8 for Method type.

What is your testing strategy?

N/A

Is this related to any issues?

N/A

Does this change need documentation?

• Explain usage of method id in /rpc endpoint docs.surrealdb.com#518

Have you read the Contributing Guidelines?

• I have read the Contributing Guidelines

[phughk]

This is really useful thanks so much for this!
LGTM as far as I can see. We might want a test in http_integration.rs for this. Will circle in the team. If you are able to add the test then I think that would be perfect.
Just started the build on it, so assuming its green

[Odonno]

What do you think @phughk?

I could write theory tests as long as a test for each rpc method. Not sure if that would be too much.

[phughk]

We have had a chat internally with @naisofly and agreed it's ok to merge without a test, but then we will add a test for it once it is merged 👍 Pinging engineering for another tick

[phughk]

This ticket is waiting on feedback from @tobiemh , as adding it means we have 2 branches of implementation which could lead to unexpected problems.