test: cover nested watchdog suppression

[sanjeebdas1979]

Summary

Add a regression test for nested watchdog suppression guards.

The test verifies that:

• watchdog suppression starts disabled
• creating an outer guard enables suppression
• creating an inner guard keeps suppression enabled
• dropping the inner guard does not re-enable the watchdog
• suppression ends only after the final guard is dropped

Motivation

WatchdogSuppressionGuard was made counter-based so nested guards can coexist safely. This adds direct test coverage for that behavior and helps prevent regressions.

Testing

• git diff --check passes
• Standard Windows build succeeds
• cfg(msim) tests require a Unix/Linux environment because the simulator uses Unix-specific libc APIs on that code path
• Repository CI runs the sim test suite on ubuntu-latest, so the PR CI will validate this behavior in the intended environment