idiomatic error handling

[stevenctl]

What kind of change does this PR introduce?

Feature

What is the current behavior?

Users must check ClientError (and clear it?) which is a shared error for ~everything in the client rather than getting an error as part of a return value, specific to the function they just called.

• It's difficult to see which operations are fallible
• Fluent APIs/Builder pattern throws away intermediate errors rather than accumulating them, making things hard to debug

Please link any relevant issues here.

What is the new behavior?

• New methods that have a WithError suffix on PingWithError, RpcWithError and NewClientWithError that return a tuple with an error.
• Existing usage of fluent APIs continue to set ClientError to maintain backwards compat
• Execute calls will return the accumulated errors from the builder(s) rather than the shared single ClientError

Additional context

I did my best to avoid breaking existing APIs so downstream users such as supabase-go are not forced to update immediately. If the maintainers want to break the API, I'd be happy to update my own usage :)

[muratmirgun]

Thanks for contribution 🚀