Adds support for GPT-5 models

[ustincameron]

What does this PR do?

• Introduced handling for new models (gpt-5-with-ocr, gpt-5-research-with-ocr, gpt-5-mini-with-ocr, and gpt-5-nano-with-ocr) in apis.py.
• Updated config.py to include the new models in validation.
• Changed default model in main.py to gpt-5-with-ocr.
• Updated requirements.txt for greater flexibility with dependency versions.
• Bumped the version in setup.py to 1.6.0.
• Updates OpenAI client dependency to support GPT-5 API endpoints

Requirement/Documentation

• ✅ All GPT-5 variants tested and functional
• ✅ Regression testing confirms existing models still work
• ✅ Default model properly set to GPT-5
• ✅ API calls verified with correct OpenAI endpoints
• ✅ No breaking changes to existing functionality

Usage Examples

# Use new default (GPT-5)
operate --prompt "Go to [Google.com](http://google.com/)"
# Specific GPT-5 variants
operate -m gpt-5-mini-with-ocr --prompt "Open calculator"
operate -m gpt-5-nano-with-ocr --prompt "Take screenshot"
# Existing models still work
operate -m gpt-4-with-ocr --prompt "Go to GitHub"

Type of change

• New feature (non-breaking change which adds functionality)
• Tests (Unit/Integration/E2E or any other test)

Mandatory Tasks

• Make sure you have self-reviewed the code. A decent size PR without self-review might be rejected. Make sure before submmiting this PR you run tests with evaluate.py