Fix debug logging for CPU affinity bitmask

[saku3]

Description

This is an improvement addressing a potential bug in the cpu_affinity feature.

• Only logs when the DEBUG level is enabled. (It follows the behavior of runc.)
• The expression (1 << i) may interpret 1 as an i32, which could lead to a bitwise overflow.
  You can see that the original code is incorrect by running the following code:

fn main() {
    let mask = (0..usize::BITS as usize)
        .fold(0, |mask, i| mask | (1 << i));
    println!("{}", mask);   
}

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test updates
• CI/CD related changes
• Other (please describe):

Testing

• Added new unit tests
• Added new integration tests
• Ran existing test suite
• Tested manually (please provide steps)

Related Issues

Fixes #

Additional Context

[Copilot]

Pull Request Overview

This PR improves the log_cpu_affinity function by only emitting logs when the DEBUG level is enabled and by fixing potential overflow in the CPU bitmask computation.

• Added a guard (enabled!(Level::DEBUG)) to skip logging unless DEBUG is active.
• Changed the fold initial value and shift operands to usize to avoid bitwise overflow.
• Imported the enabled macro and Level from tracing.

Comments suppressed due to low confidence (2)

crates/libcontainer/src/process/cpu_affinity.rs:84

• Add a unit test for log_cpu_affinity to verify that it logs the correct mask when DEBUG level is enabled and remains silent otherwise.

    if !enabled!(Level::DEBUG) {

crates/libcontainer/src/process/cpu_affinity.rs:89

• Consider handling errors from cpuset.is_set(i) instead of using unwrap_or(false), which silently ignores potential failures. You could propagate the error with ? or log it for better visibility.

        .filter(|&i| cpuset.is_set(i).unwrap_or(false))