Fix test_change_tools_after_init test

[suryabdev]

Fix for #1572

Re-implemented the skipped test_change_tools_after_init tests

• Changed TestToolCallingAgent/test_change_tools_after_init to use a ToolCallingAgent instead of a CodeAgent
• Replace fake_tool with a tool of the same name

Testing

Ran the test multiple times using the pytest-repeat plugin

> pytest --count=50 tests/test_agents.py::TestCodeAgent::test_change_tools_after_init
=================================================================== test session starts ====================================================================
platform linux -- Python 3.12.3, pytest-8.4.2, pluggy-1.6.0 -- /home/suryab/coda/venv/smolagents/bin/python3
cachedir: .pytest_cache
rootdir: /home/suryab/coda/smolagents
configfile: pyproject.toml
plugins: anyio-4.10.0, timeout-2.4.0, repeat-0.9.4, datadir-1.8.0
collected 50 items

tests/test_agents.py::TestCodeAgent::test_change_tools_after_init[1-50] PASSED
tests/test_agents.py::TestCodeAgent::test_change_tools_after_init[2-50] PASSED
0.01s call     tests/test_agents.py::TestCodeAgent::test_change_tools_after_init[34-50]

(100 durations < 0.005s hidden.  Use -vv to show these durations.)
==================================================================== 50 passed in 0.79s ====================================================================

> pytest --count=50 tests/test_agents.py::TestToolCallingAgent::test_change_tools_after_init
=================================================================== test session starts ====================================================================
platform linux -- Python 3.12.3, pytest-8.4.2, pluggy-1.6.0 -- /home/suryab/coda/venv/smolagents/bin/python3
cachedir: .pytest_cache
rootdir: /home/suryab/coda/smolagents
configfile: pyproject.toml
plugins: anyio-4.10.0, timeout-2.4.0, repeat-0.9.4, datadir-1.8.0
collected 50 items

tests/test_agents.py::TestToolCallingAgent::test_change_tools_after_init[1-50] PASSED
tests/test_agents.py::TestToolCallingAgent::test_change_tools_after_init[2-50] PASSED
...
0.01s call     tests/test_agents.py::TestToolCallingAgent::test_change_tools_after_init[16-50]

(100 durations < 0.005s hidden.  Use -vv to show these durations.)
==================================================================== 50 passed in 0.52s ====================================================================

And ran all tests in the file

> pytest tests/test_agents.py
=================================================================== test session starts ====================================================================
platform linux -- Python 3.12.3, pytest-8.4.2, pluggy-1.6.0 -- /home/suryab/coda/venv/smolagents/bin/python3
cachedir: .pytest_cache
rootdir: /home/suryab/coda/smolagents
configfile: pyproject.toml
plugins: anyio-4.10.0, timeout-2.4.0, repeat-0.9.4, datadir-1.8.0
collected 94 items

tests/test_agents.py::TestAgent::test_fake_toolcalling_agent PASSED
...
0.01s call     tests/test_agents.py::TestAgent::test_setup_agent_with_empty_toolbox

(211 durations < 0.005s hidden.  Use -vv to show these durations.)
============================================================== 94 passed, 1 warning in 12.26s ==============================================================

[suryabdev]

For

Test is not properly implemented (GH-1255) because fake_tools should have the same name.

Is this the expected change? Should I use the class method instead to create a fake tool with the same name?
If I understand correctly we want to replace an existing tool
https://huggingface.co/docs/smolagents/en/tutorials/tools#manage-your-agents-toolbox

[suryabdev]

In #1571, it was mentioned that the tests were flaky

even though they may pass or fail inconsistently.

Do you remember the error message in the failed runs? I ran the tests multiple times (Ran the entire tests/test_agents.py file a few times, mentioned details in the PR description). test_change_tools_after_init used to always pass

[suryabdev]

cc: @albertvillanova (For review)
Added some questions, Please take a look when you are free