Expands support for Anthropic thinking & Adds support for effort. - #211

Hi @ActuallyTaylor. Thanks for splitting this out so quickly. A few things before it can go in:

• service_tier stopped being sent — the if let serviceTier block got dropped when the thinking block was rewritten. Could you restore it?
• The wire value for extra-high effort is xhigh (all lowercase), so case extraHigh = "xHigh" will be rejected by the API.
• swift format lint --strict --recursive . fails on trailing whitespace and a few long lines. swift format --in-place --recursive . should clear it.
• The stream: parameter on createMessageParams isn't used by either call site (streaming sets params["stream"] itself), so it can go.
• Tiny: ThinkingDelta should conform to Sendable, not SendableMetatype.

Decoding thinking_delta and signature_delta without yielding them yet is fine for this PR; surfacing them can follow the #103 shape. As discussed on #176, this goes in with the next minor since Thinking.init changes shape.