tensor.md missing methods

[Terminay]

docs/api-reference/tensor.md does not document tanh(), leaky_relu(), gelu(), visualize(), visualize_dot(), or grad_check()
all of which exist in leanpass/tensor.py.

[github-actions]

The issue highlights that docs/api-reference/tensor.md is missing documentation for several methods (tanh(), leaky_relu(), gelu(), visualize(), visualize_dot(), and grad_check()) that are implemented in leanpass/tensor.py.