[Bug fix] add cachetools as a dependency

[redartera]

Why are the changes needed?

In #3307, the use of the cachetools library was introduced, however that library isn't specified by flytekit as a direct dependency.

This would then cause the following error:

Traceback (most recent call last):
  File "/root/.venv/bin/pyflyte-fast-execute", line 4, in <module>
    from flytekit.bin.entrypoint import fast_execute_task_cmd
  File "/root/.venv/lib/python3.13/site-packages/flytekit/__init__.py", line 119, in <module>
    from flytekit.core.array_node_map_task import map_task
  File "/root/.venv/lib/python3.13/site-packages/flytekit/core/array_node_map_task.py", line 14, in <module>
    from flytekit.core.array_node import array_node
  File "/root/.venv/lib/python3.13/site-packages/flytekit/core/array_node.py", line 6, in <module>
    from flytekit.core import interface as flyte_interface
  File "/root/.venv/lib/python3.13/site-packages/flytekit/core/interface.py", line 30, in <module>
    from flytekit.core.type_engine import TypeEngine, UnionTransformer
  File "/root/.venv/lib/python3.13/site-packages/flytekit/core/type_engine.py", line 24, in <module>
    from cachetools import LRUCache
ModuleNotFoundError: No module named 'cachetools'

What changes were proposed in this pull request?

Just adding cachetools to pyproject.toml

[kevinddchen]

Thank you for the fix. This is breaking my Flyte docker builds, since the new version of google-auth==2.47.0 was released which drops the cachetools dependency.