[Rust][Errors] Map C failures to a focused Rust error type

[utilForever]

Parent: #137

Goal

Convert native status codes and thread-local diagnostics into structured Results.

Scope

• Define stable variants for broad C error categories
• Capture the diagnostic message at the failing call
• Implement Display and Error

Non-goals

• One error variant per function
• Panicking on user input
• Exposing thread-local pointers

Acceptance criteria

• Public safe methods return Result for recoverable failures.
• Messages survive subsequent native calls.
• Unknown future codes remain representable.

Verification

Add tests for invalid handles through sys, invalid maps, invalid directions, buffers, snapshots, and unknown codes.