Move cachetools to base deps

[r4victor]

The PR fixes cachetools being listed as server dependencies, although it's a part of a base installation too. pip install dstack (without extras) was broken starting from 0.19.0.

✗ uvx dstack
Traceback (most recent call last):
  File "/Users/r4victor/.local/share/uv/tools/dstack/bin/dstack", line 4, in <module>
    from dstack._internal.cli.main import main
  File "/Users/r4victor/.local/share/uv/tools/dstack/lib/python3.11/site-packages/dstack/_internal/cli/main.py", line 7, in <module>
    from dstack._internal.cli.commands.apply import ApplyCommand
  File "/Users/r4victor/.local/share/uv/tools/dstack/lib/python3.11/site-packages/dstack/_internal/cli/commands/__init__.py", line 8, in <module>
    from dstack._internal.cli.services.completion import ProjectNameCompleter
  File "/Users/r4victor/.local/share/uv/tools/dstack/lib/python3.11/site-packages/dstack/_internal/cli/services/completion.py", line 11, in <module>
    from dstack.api import Client
  File "/Users/r4victor/.local/share/uv/tools/dstack/lib/python3.11/site-packages/dstack/api/__init__.py", line 22, in <module>
    from dstack.api._public import BackendCollection, Client, RepoCollection, RunCollection
  File "/Users/r4victor/.local/share/uv/tools/dstack/lib/python3.11/site-packages/dstack/api/_public/__init__.py", line 3, in <module>
    import dstack._internal.core.services.api_client as api_client_service
  File "/Users/r4victor/.local/share/uv/tools/dstack/lib/python3.11/site-packages/dstack/_internal/core/services/api_client.py", line 5, in <module>
    from dstack.api.server import APIClient
  File "/Users/r4victor/.local/share/uv/tools/dstack/lib/python3.11/site-packages/dstack/api/server/__init__.py", line 11, in <module>
    from dstack.api.server._backends import BackendsAPIClient
  File "/Users/r4victor/.local/share/uv/tools/dstack/lib/python3.11/site-packages/dstack/api/server/_backends.py", line 5, in <module>
    from dstack._internal.core.backends.models import (
  File "/Users/r4victor/.local/share/uv/tools/dstack/lib/python3.11/site-packages/dstack/_internal/core/backends/__init__.py", line 1, in <module>
    from dstack._internal.core.backends.base.compute import (
  File "/Users/r4victor/.local/share/uv/tools/dstack/lib/python3.11/site-packages/dstack/_internal/core/backends/base/compute.py", line 13, in <module>
    from cachetools import TTLCache, cachedmethod
ModuleNotFoundError: No module named 'cachetools'