Allow NumPy 2 in dependency metadata

[CharlelieLrt]

Description

This PR removes the numpy<2.0.0 dependency constraint so FastGen can install
alongside packages that require NumPy 2. In particular, it allows the
PhysicsNeMo diffusion-fastgen extra to resolve without weakening PhysicsNeMo's
NumPy dependency.

The change affects dependency metadata only. It does not change training
methods or public APIs, and it remains independent of the loss-hook proposal
in FastGen #44.

Dependencies

• Depends on

  • This PR starts from FastGen main and has no prerequisite PR.

• Depends on this PR

  • PhysicsNeMo #2096 adds private adapters and public sCM and MeanFlow losses. Its dependency pin includes this metadata change without waiting for an upstream merge.

• Later follow-ups

  • PhysicsNeMo #2097 extends the loss API to DMD2 and f-distill.
  • PhysicsNeMo #2098 adds checkpoint bundles for restarting distillation.
  • PhysicsNeMo #2099 adds the optional training strategy and the grouped changelog entry.

• Related prerequisites

  • PhysicsNeMo #2094 adds named diffusion inputs and outputs.
  • PhysicsNeMo #2095 adds inverse SNR and TrigFlow components.

• Independent proposal

  • FastGen #44 provides shared loss hooks for external training loops. It does not depend on this metadata change.

• Conditional follow-up

  • PhysicsNeMo #2100 replaces local compatibility code with the proposed FastGen loss hooks. Its fork pin combines this metadata change with FastGen Add composable distillation loss hooks #44.

If FastGen maintainers decline FastGen #44, we would close PhysicsNeMo #2100.
The preceding PhysicsNeMo stack would remain available.

Review process

Reviewers can compare this PR with its immediate parent. After a parent merges,
we update the remaining branches and their PR bases to keep each diff focused.