Planned NCCL license change to Apache 2.0

[gab9talavera]

We plan to change the NCCL project license from BSD 3-Clause to the Apache License 2.0.

Why we are doing this

• Simplify the contribution and review process for both internal and external contributors.
• Align NCCL with common practice in other open-source projects that use Apache 2.0.

Impact on contributors

• Existing contributors are being contacted by email to request consent to re-license their past NCCL contributions under Apache 2.0.
• Please respond to that email if you have any questions or concerns.
• If we do not receive a response, we will review the associated commits to determine whether any additional action is needed.

Next steps

• Once the re-licensing process is complete, the repository will be updated with the Apache 2.0 license, updated CONTRIBUTING guidelines, and refreshed source headers and acknowledgements.