Add provider base URLs for computer use agents

[devin-ai-integration]

Summary

• Adds optional provider-scoped base URL fields for the three computer-use agent API key models: openai_base_url, anthropic_base_url, and google_base_url, serialized as camelCase wire keys.
• Adds shared validation for custom API key mode and absolute http/https provider base URLs across sync and async managers.
• Adds serialization and validation tests for CUA, Claude Computer Use, and Gemini Computer Use.

Review & Testing Checklist for Human

• Confirm the client-side validation behavior is desirable for SDK users, especially requiring api_keys when use_custom_api_keys is true.
• Verify backend support accepts the new apiKeys.*BaseUrl payload keys for all three endpoints.
• Try one real custom endpoint per provider once backend support is deployed.

Notes

Local checks:

• poetry install
• poetry run ruff check hyperbrowser/models/agents/cua.py hyperbrowser/models/agents/claude_computer_use.py hyperbrowser/models/agents/gemini_computer_use.py hyperbrowser/client/managers/agents_validation.py hyperbrowser/client/managers/sync_manager/agents/cua.py hyperbrowser/client/managers/sync_manager/agents/claude_computer_use.py hyperbrowser/client/managers/sync_manager/agents/gemini_computer_use.py hyperbrowser/client/managers/async_manager/agents/cua.py hyperbrowser/client/managers/async_manager/agents/claude_computer_use.py hyperbrowser/client/managers/async_manager/agents/gemini_computer_use.py
• poetry run pytest tests/test_computer_use_wire_contract.py

poetry run ruff check . was attempted and fails on pre-existing unrelated issues in files not touched by this PR.

Link to Devin session: https://app.devin.ai/sessions/1ed16d43e37049e8958d37729e8fd6d0
Requested by: @shrisukhani

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.