Add Workflow random streams and read-only detection

[patbeqo]

What changed?

• Added experimental named deterministic Random streams through Workflow.getRandomStream(String).
• Streams are independent by name and from existing Workflow randomness.
• Streams replay deterministically, reseed after a Workflow Reset boundary, and use a new sequence for each Run.
• Added experimental WorkflowUnsafe.isReadOnly().
• Added coverage for seed stability, named-stream independence, replay, Reset, Continue-As-New, run and child isolation, and read-only Workflow contexts.

Why?

OpenTelemetry and other integrations need replay-stable entropy without perturbing a Workflow's application random sequence, plus a way to avoid draws where Workflow state cannot be mutated. This is the prerequisite slice for #3046.

Breaking changes?

None. The public APIs are additive and experimental.

Server PR

None.

Test plan

• mise exec -- ./gradlew :temporal-sdk:test --offline
• mise exec -- ./gradlew test --offline
• mise exec -- ./gradlew spotlessCheck
• mise exec -- ./gradlew :temporal-sdk:javadoc --offline

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-16T14:28:37.654563Z	5193120	Draft marked ready

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Codex Review: Didn't find any major issues. What shall we delve into next?

Reviewed commit: 519312060f

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