Non-idempotent names in BoringUtils() break chisel-testers2 caching

**Type of issue**: bug report

**Other information**

Tests run in parallel will not have predictable names from BoringUtils.bore() as the name picked for the signal is based on an increasing counter shared across threads.

**If the current behavior is a bug, please provide the steps to reproduce the problem:**

**What is the current behavior?**

BoringUtils.bore() names can vary in tests depending on whether they are run in serial or in parallel.

**What is the expected behavior?**

BoringUtils.bore() should be idempotent: it shouldn't matter how you invoke the tests.

**Please tell us about your environment:**

v3.5.0-RC2

**What is the use case for changing the behavior?**

Caching should work when running tests in parallel.

Start by locating the BoringUtils.bore implementation and the tests that exercise chisel-testers2 caching. Compare names produced when tests run serially and in parallel; done means bore names are deterministic regardless of test execution order and caching remains reliable.

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