Relax `==` version requirements on dependencies

[jiawen]

Describe the bug
nerfstudio lists a handful of dependencies using equality constraints, e.g., timm==0.6.7. This makes it hard to use nerfstudio in a project that also uses a newer version of some of those dependencies (e.g., timm==0.9.1).

To Reproduce
Steps to reproduce the behavior:
uv pip install nerfstudio==1.1.5 timm==0.9.1

Expected behavior
Relaxed version requirements. We can use ~= or >= as appropriate.

As of this issue report, the list is:

    "nerfacc==0.5.2",
    "opencv-python-headless==4.10.0.84",
    "splines==0.3.0",
    "viser==1.0.0",
    "timm==0.6.7",
    "gsplat==1.4.0",