151 fix: added agents unit tests

[ParallelVoid]

This PR adds new test files to the agents module with the goal of increasing test coverage in total for the project. The test coverage for the agents folder went up from 34% to 87%:

• initially:

Name                           Stmts   Miss  Cover
--------------------------------------------------
fenn/agents/__init__.py          144     54    62%
fenn/agents/agent.py              22     22     0%
fenn/agents/llm.py                94     39    59%
fenn/agents/node.py               45     45     0%
fenn/agents/rag/__init__.py        3      0   100%
fenn/agents/rag/chunker.py        44     28    36%
fenn/agents/rag/llm.py            92     92     0%
fenn/agents/rag/loader.py         98     68    31%
fenn/agents/rag/rag.py            70     57    19%
fenn/agents/rag/rag_node.py       28      0   100%
fenn/agents/rag/retriever.py     207    146    29%
fenn/agents/tools.py              18     18     0%
--------------------------------------------------

• now:

Name                           Stmts   Miss  Cover
--------------------------------------------------
fenn/agents/__init__.py          144      0   100%
fenn/agents/agent.py              22      0   100%
fenn/agents/llm.py                94      1    99%
fenn/agents/node.py               45      0   100%
fenn/agents/rag/__init__.py        3      0   100%
fenn/agents/rag/chunker.py        44      0   100%
fenn/agents/rag/llm.py            92      0   100%
fenn/agents/rag/loader.py         98     38    61%
fenn/agents/rag/rag.py            70      0   100%
fenn/agents/rag/rag_node.py       28      0   100%
fenn/agents/rag/retriever.py     207     77    63%
fenn/agents/tools.py              18      0   100%
--------------------------------------------------

Also added more tests to tests/unit/vision/test_resize.py.

[ApusBerliozi]

@ParallelVoid, hello mate

Thx for your work! Kindly check why tests are failing