Performance: reduce per-call SHA1 allocation for deterministic orchestration GUIDs

1. What is the issue?

Each call to the deterministic orchestration NewGuid() implementation creates and disposes a new SHA1 HashAlgorithm instance.

2. Likely priority

Low. It affects orchestrations that use context.NewGuid() frequently, including some entity correlation paths, but other per-call allocations are likely larger.

3. Impact on performance

Repeated hash-algorithm construction adds allocation and disposal overhead during orchestration replay. The cost scales with the number of deterministic GUIDs generated per execution.

4. Details and code reference

Deterministic GUID implementation:

https://github.com/microsoft/durabletask-dotnet/blob/883211a3a7ab0b55bb90b9c9e498148e4d65ead9/src/Worker/Core/Shims/TaskOrchestrationContextWrapper.cs#L403-L458

SHA1 creation is here:

https://github.com/microsoft/durabletask-dotnet/blob/883211a3a7ab0b55bb90b9c9e498148e4d65ead9/src/Worker/Core/Shims/TaskOrchestrationContextWrapper.cs#L437-L446

5. Guidance for how to fix

Treat this as replay-compatibility-sensitive. Any reuse or replacement must produce byte-for-byte identical GUIDs for existing instance ID, timestamp, and counter inputs across supported target frameworks. Prefer an isolated optimization with deterministic-value regression tests before and after the change; do not change the namespace, hash input, byte ordering, SHA1 algorithm, or version-bit handling.

Start in src/Worker/Core/Shims/TaskOrchestrationContextWrapper.cs, especially the deterministic GUID implementation and SHA1 creation around lines 403-458. Compare the current behavior across supported target frameworks and add or run deterministic-value regression tests. Done means reducing the per-call allocation while preserving byte-for-byte identical GUIDs, including namespace, hash input, byte ordering, SHA1, and version bits.