Fix Temporal replay span parent propagation

[Thibault Soubeste (thibaultsoubeste)]

Fix Temporal replay parent propagation for workflows that schedule work after replay.

What was happening:

• Workflow spans are intentionally not emitted again during replay.
• The outbound workflow interceptor still needs the workflow span context when it injects Braintrust headers into later activity, local activity, and child workflow commands.
• After replay, for example after worker cache eviction, newly scheduled activity spans could attach outside the temporal.workflow.<Workflow> span.

Fix:

• Add a Temporal patch marker for the new replay-safe propagation path.
• Use stable per-run workflow span ids keyed by Temporal namespace, workflow type, workflow id, and run id.
• Rebuild the workflow span context during replay, and use the same rebuilt context during the original execution so the propagated Braintrust header shape stays consistent.
• Add a regression workflow that forces replay with max_cached_workflows=0, resumes by signal, and checks post-replay activities stay under the single workflow span both with and without a client parent.

[Abhijeet Prasad (AbhiPrasad)]

hey Thibault Soubeste (@thibaultsoubeste) thank you for the PR! I will review this tomorrow and work on getting it merged + released asap afterwards.