OPT:from_base_le recursion depth check

[prestwich]

as of #277 from_base_le uses recursion to stack allocate the contents of an iterator. However, there's no check on the recursion depth, allowing arbitrary-length iterators to be unpacked onto the stack. Extremely large iterators will overflow the stack this way. It also may unpack far more iterator items than the Uint can fit

• Compute the maximum iterations using BITS and base
• Pass a recursion depth and increment at each recursing layer
• Once the recursion has reached a depth where the target BITS cannot fit the number of digits in base, return an error