[Sangho Lee (sangho2)]

This PR adds support for thread-level parallelism, allowing multiple threads of a process to run concurrently on different CPUs. It introduces fine-grained cross-CPU TLB shootdowns, scheduler changes, and pinned pages for data transfers between user threads and kernel brokers to minimize TLB tracking effort. Currently, it only parallelizes user-level executions: kernel entries are still serialized.

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

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--- failure enum_variant_added: enum variant added on exhaustive enum ---

Description:
A publicly-visible enum without #[non_exhaustive] has a new variant.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#enum-variant-new
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.51.0/src/lints/enum_variant_added.ron

Failed in:
  variant Ipi:FlushTlb in /home/runner/work/litebox/litebox/litebox_platform_vm_kernel/src/cpu.rs:83

--- failure exported_function_return_value_added: exported fn return value added ---

Description:
An exported function that previously returned `()` now returns a value, changing its ABI. For example, it may now require an additional register with which to return its value.
        ref: https://doc.rust-lang.org/reference/items/external-blocks.html#abi
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.51.0/src/lints/exported_function_return_value_added.ron

Failed in:
  external_interrupt_handler_impl exported as external_interrupt_handler_impl in /home/runner/work/litebox/litebox/litebox_platform_vm_kernel/src/arch/x86/interrupts.rs:167

--- failure function_missing: pub fn removed or renamed ---

Description:
A publicly-visible function cannot be imported by its prior path. A `pub use` may have been removed, or the function itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.51.0/src/lints/function_missing.ron

Failed in:
  function litebox_platform_vm_kernel::with_user_faults, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-ulitebox/d35cf77c91a0c7ed7cb0dbde471861818561151e/litebox_platform_vm_kernel/src/lib.rs:1156

--- failure constructible_struct_adds_field: struct exhaustively constructible through public API adds field ---

Description:
A pub struct that could be exhaustively constructed with a literal using only public API has a new pub field, breaking existing exhaustive literals.
        ref: https://doc.rust-lang.org/reference/expressions/struct-expr.html
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.51.0/src/lints/constructible_struct_adds_field.ron

Failed in:
  field ProcessConfig.give_up_once in /home/runner/work/litebox/litebox/litebox_shim_vm_kernel/src/lib.rs:115