Add jitter to matching long poll deadlines

[baekgyu-kim]

What changed?

Added up to 5% jitter to Matching long poll deadlines so empty long polls do not all expire at the same time after mass poll cancellation.
Fixes #6843.

Why?

When many long polls are cancelled or expire together, SDK workers can retry in alignment and create a synchronized polling burst. Subtracting a small randomized amount from the Matching long poll timeout spreads those retries while preserving the existing deadline buffer behavior.

How did you test it?

• built
  • Ran make bins and built all server/tool binaries successfully.
• run locally and tested manually
  • Started the server with make start and verified namespace/cluster health via Temporal CLI.
• covered by existing tests
  • Ran existing Matching empty-poll tests for workflow and activity task queues.
• added new unit test(s)
  • Added TestJitteredLongPollTimeout for deterministic jitter timeout calculation coverage.
• added new functional test(s)

Potential risks

The effective long poll timeout can be shortened by up to 5%. The jitter is bounded and does not change the existing returnEmptyTaskTimeBudget deadline buffer.