[BUG] Jax for BiphasixAxonMap silent error when rebuilt

[jgranley]

Jax removed a feature that allowed recompilation of a jit compiled function, which was used here. Now, if a BiphasicAxonMapModel with jax engine is rebuilt with a different lambda, then it will still compute according to the old lambda.

Not planning on fixing this right now, since jax's future with p2p is uncertain, but wanted to document it atleast. Could add a warning message though.