refactor : remove unnecessary conformance to Sendable Protocol

[inwoodev]

Since all the members are sendable, the WeatherClient does not need to conform to Sendable Protocol explicitly. It is implicitly Sendable.

[mbrandonw]

Good catch, thanks!

One thing to keep in mind is that if the WeatherClient ever moves to its own module it will then need to explicitly conform to Sendable. The implicit conformance only works in the same module the type is defined in.