SDKs should expose Nexus request deadline

Describe the solution you'd like

All SDKs should make the "request deadline" available in the Nexus context. Note, this is intentionally deadline and not timeout (even though it's derived from request timeout header) because deadline is more useful. Ideally this is called "request deadline" and not just "deadline" which can ambiguously mean operation deadline or fetch result deadline.

Per-SDK Tickets

Nexus SDK

• Go - Already in context
• Java - Already exists
• TypeScript - https://github.com/nexus-rpc/sdk-typescript/issues/27
• Python - https://github.com/nexus-rpc/sdk-python/issues/29
• .NET - https://github.com/nexus-rpc/sdk-dotnet/issues/13

Temporal SDK

• Go - Already in context
• Java - TODO
• Core - TODO - needs to expose deadline to langs (already has request-timeout parser logic)
• TypeScript - TODO - after Core
• Python - TODO - after Core
• .NET - TODO - after Core
• Ruby - TODO - no Nexus yet
• PHP - TODO - no Nexus yet
• Temporal CLI - N/A

Start with the Core request-timeout parser logic mentioned in the issue, then review the unchecked Temporal SDK entries, beginning with Java and Core. The linked per-SDK tickets show completed Nexus SDK work and remaining language-specific scope. Done means exposing a clearly named request deadline in the Nexus context for each applicable Temporal SDK.