Implement TimeProvider for LinuxKernel platform using monotonic clock

[CvvT]

The kernel platform implements system time using the initial system time from the host + monotonic clock. The computed time may not be accurate but should be fine for now. For simplicity, I enabled clock_gettime in snp driver, but the initial value could be passed though boot parameters (hence no need for another interface).

Also added a minor fix to simplify the futex block_or_maybe_timeout logic.

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

Click for details

--- failure trait_method_added: pub trait method added ---

Description:
A non-sealed public trait added a new method without a default implementation, which breaks downstream implementations of the trait
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-new-item-no-default
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/trait_method_added.ron

Failed in:
  trait method litebox_platform_linux_kernel::HostInterface::current_system_time in file /home/runner/work/litebox/litebox/litebox_platform_linux_kernel/src/lib.rs:412

--- failure tuple_struct_to_plain_struct: tuple struct changed to plain struct ---

Description:
A publicly-visible, exhaustive tuple struct with pub fields changed to normal (curly-braces) struct, which cannot be constructed using the same struct literal syntax.
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.46.0/src/lints/tuple_struct_to_plain_struct.ron
Failed in:
  struct SystemTime in /home/runner/work/litebox/litebox/litebox_platform_linux_kernel/src/lib.rs:223