Import error when running the example.

[hzhangxyz]

To reproduce:

• uv venv
• uv pip install egglog
• uv run python main.py

where main.py:

from __future__ import annotations
from egglog import *


class Num(Expr):
    def __init__(self, value: i64Like) -> None: ...

    @classmethod
    def var(cls, name: StringLike) -> Num:  ...

    def __add__(self, other: Num) -> Num: ...

    def __mul__(self, other: Num) -> Num: ...

egraph = EGraph()

expr1 = egraph.let("expr1", Num(2) * (Num.var("x") + Num(3)))
expr2 = egraph.let("expr2", Num(6) + Num(2) * Num.var("x"))

@egraph.register
def _num_rule(a: Num, b: Num, c: Num, i: i64, j: i64):
    yield rewrite(a + b).to(b + a)
    yield rewrite(a * (b + c)).to((a * b) + (a * c))
    yield rewrite(Num(i) + Num(j)).to(Num(i + j))
    yield rewrite(Num(i) * Num(j)).to(Num(i * j))

egraph.saturate()
egraph.check(expr1 == expr2)
egraph.extract(expr1)

What get:

Traceback (most recent call last):
  File "/home/hzhangxyz/Cloud/Desktop/ddss/main.py", line 2, in <module>
    from egglog import *
  File "/home/hzhangxyz/Cloud/Desktop/ddss/.venv/lib/python3.13/site-packages/egglog/__init__.py", line 7, in <module>
    from .builtins import *  # noqa: UP029
    ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/hzhangxyz/Cloud/Desktop/ddss/.venv/lib/python3.13/site-packages/egglog/builtins.py", line 16, in <module>
    import cloudpickle
ModuleNotFoundError: No module named 'cloudpickle'

Why?

cloudpickle is currently placed in optional deps, but it seems not "optional".