!proc: add schedGet and schedSet syscalls

[adamgreloch]

TASK: RTOS-1364

Description

Motivation and Context

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (refactoring, style fixes, git/CI config, submodule management, no code logic changes)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: (list targets here).

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[gemini-code-assist]

Code Review

This pull request introduces the schedGet and schedSet system calls, refactors proc_threadPriority to support targeting arbitrary threads, and updates syscalls_schedInfo to allow querying other processes. However, several critical issues were identified in the review: a potential kernel crash due to a NULL pointer dereference in syscalls_schedGet when a thread is not found; ready queue corruption in proc_threadPriority when modifying the priority of a non-running READY thread; a potential kernel panic in proc_schedGet caused by writing to a user-space pointer while holding a spinlock; and logical errors in both syscalls_schedGet and syscalls_schedSet where the calling thread is incorrectly targeted instead of the foreign process's main thread when tid is zero.

[github-actions]

Unit Test Results

10 890 tests  ±0   10 220 ✅ ±0   53m 47s ⏱️ + 1m 17s
   680 suites ±0      670 💤 ±0 
     1 files   ±0        0 ❌ ±0 

Results for commit cbb5a53. ± Comparison against base commit 4b8784b.

[adamgreloch]

reverting to draft for now - will need to rethink the pid/tid relationship in the kernel for the libphoenix changes first.