refactor: Clean up browser action handling and fix linting issues

[breeznik]

PR Summary
This PR cleans up the browser action handling code and fixes some linting warnings.

Changes

• Refactored browser actions into a dictionary-based mapping for clearer structure and easier extensibility.
• Split action handling into separate functions to follow better coding practices and improve maintainability.
• Fixed unnecessary f-strings that didn’t have placeholders and printed Catched errors, resolving linter warnings.

Why

• Follows better practices for code organization and readability.
• Makes it easier to extend and maintain the code in the future.

Testing Results
All existing tests pass:

=========================== test session starts ============================
platform win32 -- Python 3.13.5, pytest-8.4.2, pluggy-1.6.0 -- C:\projects\personal\computer-use-preview\.venv\Scripts\python.exe
cachedir: .pytest_cache
rootdir: C:\projects\personal\computer-use-preview
plugins: anyio-4.11.0
collected 11 items                                                          

test_agent.py::TestBrowserAgent::test_denormalize_x PASSED            [  9%]
test_agent.py::TestBrowserAgent::test_denormalize_y PASSED            [ 18%]
test_agent.py::TestBrowserAgent::test_handle_action_click_at PASSED   [ 27%]
test_agent.py::TestBrowserAgent::test_handle_action_navigate PASSED   [ 36%]
test_agent.py::TestBrowserAgent::test_handle_action_open_web_browser PASSED                                                            [ 45%]
test_agent.py::TestBrowserAgent::test_handle_action_scroll_document PASSED                                                             [ 54%]
test_agent.py::TestBrowserAgent::test_handle_action_type_text_at PASSED                                                                [ 63%]
test_agent.py::TestBrowserAgent::test_handle_action_unknown_function PASSED                                                            [ 72%]
test_agent.py::TestBrowserAgent::test_multiply_numbers PASSED                                                                          [ 81%]
test_agent.py::TestBrowserAgent::test_run_one_iteration_no_function_calls PASSED                                                       [ 90%]
test_agent.py::TestBrowserAgent::test_run_one_iteration_with_function_call PASSED                                                      [100%]

============================================================ 11 passed in 12.25s ============================================================ 

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