[nnx] add PrefixMapping

[cgarciae]

What does this PR do?

Adds the PrefixMapping API to allow different "Lift Symbols" to result in the same consistent aliasing by checking the value each Variable resolves to at runtime. For example, the following code would previously be treated as inconsistent as m is passed the prefixes 0, sa1, and sa2 in in_axes, and these prefixes are not the same value. However, now this program is accepted as its evaluated that the kernel and bias Variables on m are being vectorized in axes 0 by all arguments 0, sa1, and sa2, resulting in a consistent aliasing.

m = nnx.Linear(3, 3, rngs=nnx.Rngs(0))

sa1 = nnx.StateAxes({...: 0})
sa2 = nnx.StateAxes({nnx.Param: 0})
@nnx.vmap(in_axes=(0, sa1, sa2))
def f(m1, m2, m3):
  pass

f(m, m, m)