Test and Implement optimised `filter_jit`

[LouisDesdoigts]

Allow input of a parameter list, and partition/combine around this to make all but the parameters of interest 'static'.

This needs testing to see if anything is actually gained, and if this solves the string parameter issue.

from jax import Array
import zodiax as zdx

class Foo(zdx.Base):
    leaf : Array
    unit : str

    def __call__(self, new_unit: str):
        new_value = convert(self.leaf, self.unit, new_unit) # some simple unit conversion function
        return self.set(('leaf', 'unit'), (new_value, new_unit))

param = 'leaf'
@zdx.filter_jit(param)
@zdx.filter_grad(param)
def f(pytree):
    return pytree('nm').leaf**2