Review comments

[patnebe]

Context

• Address review comments from Test resuming a process #9

Changes

• Fix error message construction in the error path
• Handle self-assignment in the move assignment operator

Test Plan

• CI

[Copilot]

Pull Request Overview

This PR addresses review comments from a previous pull request by fixing two implementation issues in the Process class. The changes improve error handling and ensure proper move semantics.

• Fix error message construction to avoid potential issues with stringstream usage in error paths
• Add self-assignment check to the move assignment operator to prevent undefined behavior

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