[PyTorch] Stop storing fused weight tensor in linear modules (NVIDIA#719

)

* Support noop concat without providing full tensor

Stop storing fused buffers in linear modules.

Signed-off-by: Tim Moon <tmoon@nvidia.com>

* Debug noop cat func

Signed-off-by: Tim Moon <tmoon@nvidia.com>

* Construct TE modules in tests with correct dtypes

Signed-off-by: Tim Moon <tmoon@nvidia.com>

* Add tolerances to numerical tests

Signed-off-by: Tim Moon <tmoon@nvidia.com>

* Use plain PyTorch concat when exporting to ONNX

Signed-off-by: Tim Moon <tmoon@nvidia.com>

---------

Signed-off-by: Tim Moon <tmoon@nvidia.com>
Signed-off-by: Tim Moon <4406448+timmoon10@users.noreply.github.com>
Co-authored-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>
Signed-off-by: Pawel Gadzinski <pgadzinski@nvidia.com>