Add setitimer/getitimer

[CvvT]

Implement syscalls setitimer and getitime, but setitimer does not support periodic timers yet (i.e., it is equivalent to alarm for now).

Also add a new feature alarm_fallback to enable/disable the fallback alarm check.

[wdcui]

LGTM. Thanks.

[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/v0.47.0/src/lints/enum_no_repr_variant_discriminant_changed.ron

Failed in:
  variant SyscallRequest::Statx 98 -> 99 in /home/runner/work/litebox/litebox/litebox_common_linux/src/lib.rs:2380