Automatically set trust_input=True when function has no inputs

[ricardoV94]

Description

I still see some tiny overhead even in functions without inputs:

import pytensor
import pytensor.tensor as pt

fn = pytensor.function([], pt.zeros((5)))
%timeit fn()  # 4.76 µs ± 190 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

fn.trust_input=True
%timeit fn()  # 2.39 µs ± 91.9 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

Probably because trust_input avoids entering some loops.