Add 2GB limitation for grouped conv bwd weight

[bartekxk]

Proposed changes

Add 2GB limitation for grouped conv bwd weight

Checklist

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• I have added tests relevant to the introduced functionality, and the unit tests are passing locally
• I have added the test to REGRESSION_TESTS list defined at the top of CMakeLists.txt in tests/CMakeLists.txt, IF the test takes more than 30 seconds to run.
• I have added inline documentation which enables the maintainers with understanding the motivation
• I have removed the stale documentation which is no longer relevant after this pull request
• (If this change is user-facing) I have added release notes which provide the end users with a brief summary of the improvement from this pull request
• I have run clang-format on all changed files
• Any dependent changes have been merged

Discussion

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[cgmillette]

@bartekxk can we describe why there is a 2GB limitation with a comment?
Due to buffer_load? Is there a workaround planned?