Refactor: Rename _compute_new_headers to compute_merged_headers

[Leah866814]

Overview

This PR includes refactoring to improve code quality and maintainability.

Refactorings Completed

Set I (Basic Refactorings)

1. Rename Method: Renamed _compute_new_headers to compute_merged_headers in sessions.py
   • Better reflects the method's actual behavior (merging headers, not just computing new)
   • Improved method documentation
   • Location: httpie/sessions.py, line 205

Testing

• ✅ All session-related tests passing (61 tests)
• ✅ No breaking changes
• ✅ Backward compatible

Context

This PR is part of the CSCI5308 (Adv Software Development) course assignment at Dalhousie University, focusing on code refactoring and open-source contribution.

Student: Yifei Wang (B01069596)