Repinned Core to upstream main and brought the bridge up to it.

[moedash]

This PR repins temporalio/bridge/sdk-core to upstream sdk-rust main and brings the bridge up to it.

What changed?

• The bridge now builds on the Core 1.0 crates. temporalio-client gets the experimental feature.
• temporalio/api and temporalio/bridge/proto are regenerated from that Core's api tree, so upstream's drift comes in here. That includes the new nexusoperation and notificationservice packages and the cause on external signal and cancel results. It also includes the include_arguments_in_marker rename, which no Python code uses.
• The Nexus system docstrings are regenerated from the new Core WIT.
• temporal_link_to_nexus_link refuses the new upstream callback link variant, the same way it refuses batch_job. The pin forces this one, since the link oneof gained the variant.

Part of AI-198 (epic AI-37).

Why?

The old pin is an "Update api_upstream" commit that upstream main never got. The Core work for AI-198 sits on current main, so the Python side needs a bridge that compiles against it first. Nothing here is about streams or channels. It's the chore on its own, and it could go upstream as is.

How did you test it?

Link to a test plan if any -

• Unit Tests
• Staging
• End to End Tests

The bridge builds, and cargo clippy -- -D warnings and poe lint are clean. Running the poe gen-protos generators a second time leaves the tree as committed. The client, activity, workflow, Nexus, replayer, visitor and converter suites pass against the dev server the fixtures start.