Fix: Ensure UTF-8 encoding in all 'open()' statements

[sepehrrasooli]

Why are these changes needed?

This PR ensures consistent UTF-8 encoding across all file operations by adding encoding="utf-8" to all with open() statements.
This prevents potential encoding issues when running the code in different environments.

Related issue number

Closes #5566

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[sepehrrasooli]

@sepehrrasooli please read the following Contributor License Agreement(CLA). If you agree with the CLA, please reply with the following information.

@microsoft-github-policy-service agree [company="{your company}"]

Options:

• (default - no company specified) I have sole ownership of intellectual property rights to my Submissions and I am not making Submissions in the course of work for my employer.

@microsoft-github-policy-service agree

• (when company given) I am making Submissions in the course of work for my employer (or my employer has intellectual property rights in my Submissions by contract or applicable law). I have permission from my employer to make Submissions and enter into this Agreement on behalf of my employer. By signing below, the defined term “You” includes me and my employer.

@microsoft-github-policy-service agree company="Microsoft"

Contributor License Agreement

@microsoft-github-policy-service agree

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.35%. Comparing base (a701e3b) to head (82936b4).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5818   +/-   ##
=======================================
  Coverage   75.35%   75.35%           
=======================================
  Files         177      177           
  Lines       11421    11421           
=======================================
  Hits         8606     8606           
  Misses       2815     2815           

Flag	Coverage Δ
unittests	75.35% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[sepehrrasooli]

@rysweet Hey, I saw that the conflicts were resolved earlier—thanks for that! I fixed the new ones yesterday. Let me know if there’s anything else I should do before review!

[jackgerrits]

Why explicitly specify utf-8 and not rely on the default behavior? https://docs.python.org/3/library/functions.html#open

In text mode, if encoding is not specified the encoding used is platform-dependent: locale.getencoding() is called to get the current locale encoding.

EDIT: Hmm I can see the merit of just going all in on utf-8 https://peps.python.org/pep-0597/

[sepehrrasooli]

Why explicitly specify utf-8 and not rely on the default behavior? https://docs.python.org/3/library/functions.html#open

In text mode, if encoding is not specified the encoding used is platform-dependent: locale.getencoding() is called to get the current locale encoding.

EDIT: Hmm I can see the merit of just going all in on utf-8 https://peps.python.org/pep-0597/

Agreed! Explicitly setting UTF-8 ensures consistency across platforms. Let me know if any changes are needed.