feat: implement getgroups and setgroups syscalls

[wdcui]

Summary

Add support for getgroups(2) and setgroups(2) syscalls to manage supplementary group IDs.

Changes

• Add Getgroups and Setgroups variants to SyscallRequest enum
• Add supplementary_groups field to Credentials struct
• Change Task.credentials to RefCell<Arc<Credentials>> for interior mutability
• Implement sys_getgroups() and sys_setgroups() methods
• Add NGROUPS_MAX (65536) constant for validation
• Add 6 unit tests for comprehensive coverage

Error handling

• getgroups: EINVAL for negative size or buffer too small; EFAULT for invalid pointer
• setgroups: EINVAL for size > NGROUPS_MAX; EFAULT for invalid pointer

Testing

• Added 6 unit tests:
  • test_getgroups_empty - Verifies empty initial state
  • test_setgroups_and_getgroups - Verifies round-trip set/get
  • test_getgroups_einval_buffer_too_small - Buffer validation
  • test_setgroups_empty - Empty groups handling
  • test_getgroups_negative_size - Negative size validation
  • test_setgroups_too_many - NGROUPS_MAX validation

Related

This addresses P0 syscall support as mentioned in #360.

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

Click for details

--- failure enum_no_repr_variant_discriminant_changed: enum variant had its discriminant change value ---

Description:
The enum's variant had its discriminant value change. This breaks downstream code that used its value via a numeric cast like `as isize`.
        ref: https://doc.rust-lang.org/reference/items/enumerations.html#assigning-discriminant-values
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/enum_no_repr_variant_discriminant_changed.ron

Failed in:
  variant SyscallRequest::Sysinfo 82 -> 84 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2232
  variant SyscallRequest::CapGet 83 -> 85 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2235
  variant SyscallRequest::GetDirent64 84 -> 86 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2239
  variant SyscallRequest::SchedGetAffinity 85 -> 87 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2244
  variant SyscallRequest::SchedYield 86 -> 88 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2249
  variant SyscallRequest::Futex 87 -> 89 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2250
  variant SyscallRequest::Execve 88 -> 90 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2253
  variant SyscallRequest::Umask 89 -> 91 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2258
  variant SyscallRequest::Prctl 90 -> 92 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2261
  variant SyscallRequest::Alarm 91 -> 93 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2264
  variant SyscallRequest::SetITimer 92 -> 94 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2267