test: fix test aborts and hardware-dependent failures on single-core machines

[iamjaeholee]

Resolves #1473

Description

This PR fixes two test suite issues that cause cargo test --bin uhyve to fail prematurely on single-core machines.

Changes Made

1. Fixed graceful exit replacing panic! in affinity validation
The test_affinity_errors_when_lacking_cpu_cores test relies on #[should_panic].
When running on a machine with fewer cores than requested, affinity.validate() fails. However, instead of panicking, clap gracefully terminates the process via app.error().exit().
Fix: Added #[cfg(test)] panic!("{e}"); to the ValueValidation error block to properly satisfy the test harness.

2. Removed hardware-dependent logic from TOML parsing tests
Fixing the above bug exposed a flaw in test_toml_affinity_strings and test_toml_affinity_usize_array. Both tests explicitly request 3 cores (affinity = '0-1,2') and then call get_affinity() to verify logic validation. However, this implicitly triggers the hardware validation check first, which unconditionally panics on single/dual-core machines.
Fix: Removed the get_affinity() calls from these TOML tests, as the TOML deserialization itself is already verified via assert_eq!.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.53%. Comparing base (af7ba88) to head (caeca20).

Files with missing lines	Patch %	Lines
src/bin/uhyve.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1474      +/-   ##
==========================================
+ Coverage   79.38%   79.53%   +0.14%     
==========================================
  Files          39       39              
  Lines        5592     5589       -3     
==========================================
+ Hits         4439     4445       +6     
+ Misses       1153     1144       -9     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.