Improve eliminate_concat

[pfultz2]

We want to be able to insert copy operator for some concat cases where:

• Almost all the inputs are a precompile_op
• Only 1 copy is needed

To do this we need to extend the concat_optimization model to support this. One function to insert a copy and another to query if its acceptable to insert the copy.

Later, the fuse_ops pass can fuse the copies with the precompile_op(similar to find_contiguous_pointwise) when the input is only used once.