fix: install llvmlite to run tests

[HarshitaKalani]

without this:

% python -m pytest --doctest-modules --cov=./ --cov-report=html
===================================================== test session starts =====================================================
platform darwin -- Python 3.8.20, pytest-8.3.4, pluggy-1.5.0
rootdir: /Users/pranavchiku/repos/pydatastructs
configfile: pyproject.toml
plugins: cov-5.0.0
collected 190 items / 1 error                                                                                                 

=========================================================== ERRORS ============================================================
______________ ERROR collecting pydatastructs/linear_data_structures/_backend/cpp/algorithms/llvm_algorithms.py _______________
ImportError while importing test module '/Users/pranavchiku/repos/pydatastructs/pydatastructs/linear_data_structures/_backend/cpp/algorithms/llvm_algorithms.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
../../mambaforge/envs/pyds-env/lib/python3.8/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
pydatastructs/linear_data_structures/_backend/cpp/algorithms/llvm_algorithms.py:1: in <module>
    from llvmlite import ir, binding
E   ModuleNotFoundError: No module named 'llvmlite'

---------- coverage: platform darwin, python 3.8.20-final-0 ----------
Coverage HTML written to dir htmlcov

=================================================== short test summary info ===================================================
ERROR pydatastructs/linear_data_structures/_backend/cpp/algorithms/llvm_algorithms.py
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
====================================================== 1 error in 1.39s =====================================================