Enable datetime comparisons for fields with LazyExprs

[lshaw8317]

The following code throws an error since numexpr does not appear to support datetime datatype comparisons.

N = 1000
rng = np.random.default_rng(seed=1)
it = ((-x + 1, x - 2, rng.normal()) for x in range(N))
sa = blosc2.fromiter(
    it, dtype=[("time", "<M8[s]"), ("A", "f4"), ("B", "f8")], shape=(N,), urlpath="sa-1M.b2nd", mode="w"
)

expr = sa["time"] < 1000
print(expr[:]) #throws error

In addition, it would be good to support expr = sa["time < 1000"] as well (which also throws an error).