Post-init model patching fix (#280)

## Summary
- Previously, the pre-trained weights were not being loaded if patching
model post-initialization
- Instead of loading weights, just patch the model instance module's
forward method (see #279)

## Testing Done
- In convergence tests, check that pre-init patching and post-init
patching match results from original model

- Hardware Type: A100
- [x] run `make test` to ensure correctness
- [x] run `make checkstyle` to ensure code style
- [ ] run `make test-convergence` to ensure convergence --> most tests
working, waiting for other fixes for all tests to pass